25G interfaces went down after upgrading the MPX from 13.0-67.39 to 13.0-84.10. The issue goes away as soon as downgrade is done to the original version 
 
We can clearly see that that 25/x interfaces are not receiving any LACPDUs post upgrade. We only see tx packets and no rx lacpdus  :
 
Post upgrade :
 
 nsconmsg -K newnslog -g lacpdus -s disptime=1 -d current | less
Displaying performance information
NetScaler V20 Performance Data
NetScaler NS13.1: Build 9.60.nc, Date: Nov 17 2021, 08:06:36   (64-bit)
 
 
reltime:mili second between two records Sun Dec 19 13:49:32 2021
  Index   rtime totalcount-val      delta rate/sec symbol-name&device-no&time
      0    3579              1          1        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 13:49:32 2021
      1       0              1          1        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 13:49:32 2021
      2    6999              3          2        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 13:49:39 2021
      3       0              3          2        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 13:49:39 2021
      4   28000              4          1        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 13:50:07 2021
      5       0              4          1        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 13:50:07 2021
      6   28001              5          1        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 13:50:35 2021
      7       0              5          1        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 13:50:35 2021
      8   35000              6          1        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 13:51:10 2021
      9       0              6          1        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 13:51:10 2021
     10   28001              7          1        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 13:51:38 2021
     11       0              7          1        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 13:51:38 2021
     12   28001              8          1        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 13:52:06 2021
     13       0              8          1        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 13:52:06 2021
     14   28000              9          1        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 13:52:34 2021
     15       0              9          1        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 13:52:34 2021
     16   35001             10          1        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 13:53:09 2021
     17       0             10          1        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 13:53:09 2021
     18   28000             11          1        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 13:53:37 2021
     19       0             11          1        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 13:53:37 2021
     20   28001             12          1        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 13:54:05 2021
     21       0             12          1        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 13:54:05 2021
 
exec: show channel
1)      Interface LA/1 (802.3ad Link Aggregate) #19
        flags=0x41004000 <ENABLED, DOWN, AGGREGATE, down, HAMON, HEARTBEAT, 802.1q>
        MTU=1500, native vlan=1, MAC=02:e0:ed:9e:a6:4e, downtime 0h10m16s
        Requested: media NONE, speed AUTO, duplex NONE, fctl NONE,
                 throughput 0
        Actual: throughput 0
        LLDP Mode: NONE
        RX: Pkts(0) Bytes(0) Errs(0) Drops(0) Stalls(0)
        TX: Pkts(0) Bytes(0) Errs(0) Drops(0) Stalls(0)
        NIC: InDisc(0) OutDisc(0) Fctls(0) Stalls(0) Hangs(0) Muted(0)
        Bandwidth thresholds are not set.
        LA mode: AUTO
                25/1: unknown                   DOWN
                PortID=(32768,11), Mux=DETACHED, Rx=DEFAULTED, UNSELECTED
                <Active, Long timeout, Agg, Defaulted>
                Partner: SysID=(0,00:00:00:00:00:00), Key=0, PortID=(0, 0)
                        <Passive, Long timeout>
 
                25/2: unknown                   DOWN
                PortID=(32768,12), Mux=DETACHED, Rx=DEFAULTED, UNSELECTED
                <Active, Long timeout, Agg, Defaulted>
                Partner: SysID=(0,00:00:00:00:00:00), Key=0, PortID=(0, 0)
                        <Passive, Long timeout>
 
 
 
 
Post downgrade or on the original version 13.0-67.x :
 
Both rx and tx are seen :
 
[nsconmsg -K newnslog -g lacpdus -s disptime=1 -d current | less
Displaying performance information
NetScaler V20 Performance Data
NetScaler NS13.0: Build 67.39.nc, Date: Oct  7 2020, 08:37:53   (64-bit)
 
 
reltime:mili second between two records Sun Dec 19 14:25:11 2021
  Index   rtime totalcount-val      delta rate/sec symbol-name&device-no&time
      0    4087              2          2        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 14:25:11 2021
      1       0              2          2        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 14:25:11 2021
      2    7096              1          1        0 nic_tot_rx_lacpdus interface(25/1) Sun Dec 19 14:25:18 2021
      3       0              7          5        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 14:25:18 2021
      4       0              1          1        0 nic_tot_rx_lacpdus interface(25/2) Sun Dec 19 14:25:18 2021
      5       0              8          6        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 14:25:18 2021
      6    7000              3          2        0 nic_tot_rx_lacpdus interface(25/1) Sun Dec 19 14:25:25 2021
      7       0              8          1        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 14:25:25 2021
      8       0              3          2        0 nic_tot_rx_lacpdus interface(25/2) Sun Dec 19 14:25:25 2021
      9       0              9          1        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 14:25:25 2021
     10   21000              4          1        0 nic_tot_rx_lacpdus interface(25/1) Sun Dec 19 14:25:46 2021
     11       0              4          1        0 nic_tot_rx_lacpdus interface(25/2) Sun Dec 19 14:25:46 2021
     12    7000              9          1        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 14:25:53 2021
     13       0             10          1        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 14:25:53 2021
     14   21000              5          1        0 nic_tot_rx_lacpdus interface(25/1) Sun Dec 19 14:26:14 2021
     15    7000             10          1        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 14:26:21 2021
     16       0              5          1        0 nic_tot_rx_lacpdus interface(25/2) Sun Dec 19 14:26:21 2021
     17       0             11          1        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 14:26:21 2021
     18   21000              6          1        0 nic_tot_rx_lacpdus interface(25/1) Sun Dec 19 14:26:42 2021
     19    7000             11          1        0 nic_tot_tx_lacpdus interface(25/1) Sun Dec 19 14:26:49 2021
     20       0              6          1        0 nic_tot_rx_lacpdus interface(25/2) Sun Dec 19 14:26:49 2021
     21       0             12          1        0 nic_tot_tx_lacpdus interface(25/2) Sun Dec 19 14:26:49 2021
     22   21000              7          1        0 nic_tot_rx_lacpdus interface(25/2) Sun Dec 19 14:27:10 2021
     23    7000              7          1        0 nic_tot_rx_lacpdus interface(25/1) Sun Dec 19 14:27:17 2021
     24    7000
 
exec: show channel
 
1)      Interface LA/1 (802.3ad Link Aggregate) #19
        flags=0x4100c020 <ENABLED, UP, AGGREGATE, UP, HAMON, HEARTBEAT, 802.1q>
        MTU=1500, native vlan=1, MAC=02:e0:ed:9e:a6:4e, uptime 0h17m02s
        Requested: media NONE, speed AUTO, duplex NONE, fctl NONE,
                 throughput 0
        Actual: throughput 2000
        LLDP Mode: NONE
        RX: Pkts(67274) Bytes(10429481) Errs(0) Drops(27738) Stalls(0)
        TX: Pkts(80302) Bytes(15215185) Errs(0) Drops(0) Stalls(0)
        NIC: InDisc(0) OutDisc(0) Fctls(0) Stalls(0) Hangs(0) Muted(0)
        Bandwidth thresholds are not set.
        LA mode: AUTO
 
 
                25/1: FIBER-1000-FULL-OFF       UP  0h17m08s
                PortID=(32768,11), Mux=DISTRIBUTING, Rx=CURRENT, SELECTED
                <Active, Long timeout, Agg, Sync, Collecting, Distributing>
                Partner: SysID=(32768,00:9a:d2:7d:6c:80), Key=5, PortID=(32768, 563)
                        <Active, Long timeout, Agg, Sync, Collecting, Distributing>
 
                25/2: FIBER-1000-FULL-OFF       UP  0h17m08s
                PortID=(32768,12), Mux=DISTRIBUTING, Rx=CURRENT, SELECTED
                <Active, Long timeout, Agg, Sync, Collecting, Distributing>
                Partner: SysID=(32768,00:9a:d2:7d:6c:80), Key=5, PortID=(32768, 306)
                        <Active, Long timeout, Agg, Sync, Collecting, Distributing>
 
 

Problem Cause