VPX running on KVM platforms with virtio NICs may report TX stall when operating in single PE mode.

The following conditions must be met to hit this issue.
1) VPX hosted on KVM
2) Version: 13.1-45.x or later
3) 2vCPU ( single PE )
4) When the packet takes more than 4 sec to get transferred
 

We have the following workarounds:
Option 1:Versions before 13.1-45.X are not impacted. Downgrading is a temporary workaround.
Option 2: Assign more than 2 vCPUs for the VPX .
Note: We need to make sure that the license allows more than 2vCPUs).Please refer to the following license datasheet for VPX. 
https://www.netscaler.com/content/dam/netscaler/documents/data-sheet/netscaler-software-form-factors-data-sheet.pdf

As a permanent  fix , we need to upgrade to the fixed build of NSHELP-37106.

Problem Cause

This article describes an issue where VPX running on KVM platforms with virtio NICs may experience TX stalls when operating in single-PE mode