Question:
When VDA is placed into Maintenance Mode, will existing Active session present before Maintenance Mode was enabled still be able to launch new resources from that VDA?

Answer:

User connectivity is affected as follows when in maintenance mode:

• With Server OS machines, users can connect to existing sessions but cannot start new sessions.
• With Desktop OS and Remote PC Access machines, users cannot connect or reconnect once the machine is in maintenance mode. If they are already connected, then they stay connected until they next disconnect or log off.

Note: This behavior has been changed in the cloud service. See https://docs.citrix.com/en-us/citrix-virtual-apps-desktops-service/install-configure/delivery-groups-manage.html#control-session-reconnection-when-disconnected-from-machine-in-maintenance-mode for more details.