In your ThinOS 9 policy do you have the WMS group prefix, token, and server set? There is a known bug that was supposed to only be impacting WMS public cloud (I realize you’re WMS is on-prem) on https://us1.wysemanagementsuite.com but your issue sound similar to what I experienced where post upgrade I would have to hit “validate key” to get the device to check-in.
I had to setup my ThinOS 9 policy in WMS as below and for the server URL take off the https and just use us1.wysemanagementsuite.com, this works for me when going 8.6_807 to 9.1.3112 and also any version of 9.x to 9.1.3112
