I don’t know if this will help, but back in March 2020, I had a problem that sounded similar. Community member Corleone also had a similar problem. I solved the problem by turning off Bluetooth on my phone. This was with an earlier version of the Z1 firmware, so it may not be related.
Just did some more testing: Indeed, disabling Bluetooth on the mobile seems to resolve the Wifi connectivity issue - great!
This is funny, as Bluetooth on the Z1 was disabled in both cases.
Seems to be a bug in the app. Will you report this to Ricoh?
Note that in my case, I also reset all the settings on my Z1, but hopefully you don’t need to do this as there is no easy way to reset the camera with the buttons (assuming you already tried pressing and holding the power and Wi-Fi together for more than 10 seconds)