We would normally expect the print server to be able to connect to any SSID with alphanumeric characters, like the “mytest” SSID you created.
When there have been multiple units experiencing the same issue and the setup steps are being followed correctly, as you have been doing, we like to changing out external factors to the product itself to see if those may be having any effect.
The reason I recommend testing a different access point or router is because it seems that this access point has been a constant factor so far, so we want to try changing this variable.
We want to try a different model of access point if possible in case there may be something with the Aruba InstantOn AP22 you have been trying so far that is preventing the print server from being able to connect to the network which could be causing it to return to the Ad-hoc settings when it cannot establish a connection. The results of this change can help us determine what next steps we may have.
Lukas T