Hello,
I am sorry you are having a poor experience with your UDMp. There are several on the Unifi forums that have made suggestions to those who run into issues such as your self. I have a UDMP in a production setup for a small school and “knocking on wood” have not had the issues many such as your self are experiencing.
I went from 1.8.6 to 1.9.3 as the comments in the release forums had me wait a bit longer even though I had already updated the controller to 6.0.34 to support the U6 LR we installed to replace the AP-AC-LR’s. I have found, and others; that there are steps that work best for updating the firmware and controllers that yield a more stable environment. I will explain below, also only use the new GUI for what has been migrated and removed from classic, classic GUI is all I use.
First things first. Power cycle the UDMp and make a settings only back up and download a copy for use later. Do a factory reset into recover mode.
Once this is completed and the system is accessible, before restoring any settings, update the firmware to 1.9.3, once firmware is updated, before re adopting your elements restart the machine. unless you want to use a beta controller, 6.2.13 has been good for me, use the release 6.0.34 and switch and non U6 AP firmware 5.43.34.
For future, the process I use to update any equipment first thing is to power cycle any device prior to firmware update. Make a settings backup only. Reboot the device again, update, restart the device. If this is to update a UDM/usg continue (at this point a few do a factory restore then restore from the settings backup), I have not had to do that but once. It will take 10-20 minutes for all the devices to reconnect, if they do not; come back on line or show disconnected, cycle the power on the device first before you reset/ forget and re adopt them.
Also make sure you make note of your set inform user name and password so you can re adopt your network devices after the factory reset, and restore of settings.
Is it a pain in tail when it gets to the point you are experiencing, absolutely. Hopefully this will help resolve your issues and you will see a more stable experience moving forward.
Cheers.