WMS 3.1 only sees Wyse 3040 for 1 hour

We have a new WMS 3.1 server (Windows Server 2019) and have 3 test Wyse 3040 PCoIP devices that were successfully upgraded from ThinOS 8.6_606 to 9.1.1131 this week. They are on their own separate VLAN for testing. The units check in to WMS and image to the new OS without issue. However, after an hour they no longer show as powered on or in compliance. This behavior survives restarting the devices and the server. Does anyone have any idea what could be causing this? Thanks for your help!