@embeddedmz , did you try to follow this instructions?
https://forums.ubports.com/topic/6951/ubports-quick-and-simple-install-on-xiaomi-mi-a2
I was in same sittuation, phone I bought had Android 10 but I downgraded it following tutorial I linked above.
@embeddedmz you are correct. I see same after reading your reply.
I am not able to say if this problem came with recent ota-21 update as I did not use BT before but niw I,see same problem you describe (including toggle goin back to disabled)
@embeddedmz , not sure if root cause is same but I had same problem. On other chat I found some people saying issue could be in USB 3 port. I switched from my Ubuntu laptop (which I experience problem at same stage) to Mac from 2015 and ubports installer managed did the job there 
not sure if that helps..
This guide worked well for me.
Unfortunately I could not install Ubuntu at the end ( installer was getting <waiting for device> error due to fastboot crashing after downgrade to Andreoid 9). On some other articles people were suggesting it could be USB Port issue, that may be true actually. As I had no other idea I installed "installer" on other laptop (switched from Ubuntu to Mac) and there it worked..
@taiga-woods (all), If you look for great battery life experience, I can tell that I also have UT on Xiaomi MI A2. I do not use it much apart of reading news each evening but device (connected to wifi all the time) stays alive for 100 hours and more. Just FYI 
@martinm , I confirm what others said. I recently bought Nexus 5 in order to install UT and I tested battery for a week to know condition, it was able to run (idle) for 2 days while on UT it is max 12 hours.
@bogotrax please disable wifi before starting waydroid. If all works on cellular data for you (does for me)I would call it known problem reported in other threads mi a2 related...
@branja6 did you managed to have UT at the end.? Thread is old and I see no XA2 on official list, so I guess it was not ported?
Thx
@stanwood , I think MI A2 WIFI problem is not only when using Google Apps, I have phone crashing each time when trying to open DuckDuckGo or MS Edge (all works when WIFI disabled an phone is on LTE).
Btw. When going thru list of fully functional devices, I see this is not properly mentioned on https://devices.ubuntu-touch.io/ (all those have "?" next to Waydroid feature). Would you know where to report it?
@embeddedmz you are correct. I see same after reading your reply.
I am not able to say if this problem came with recent ota-21 update as I did not use BT before but niw I,see same problem you describe (including toggle goin back to disabled)
@embeddedmz could it be that your device finds devices without name?
I see some like that too but also named ones on same list..
@embeddedmz , not sure if root cause is same but I had same problem. On other chat I found some people saying issue could be in USB 3 port. I switched from my Ubuntu laptop (which I experience problem at same stage) to Mac from 2015 and ubports installer managed did the job there
not sure if that helps..
@c4pp4 , you mean both on WIFI or Cellular Data?
I can play with more apps next days maybe but for sure browsers I tried crash device, I tried to look into waydroid's log but I did not see any exception (could be I must search harder as each restart and run puts new logs I guess).
In case I will have more detailed debug results, I will post here (for now I can use device without WIFI as well)
@c4pp4 , sorry for late reply.
it is actually interesting - could be that my assumption about WIFI is not exactly valid.
I tried MS Edge (browser) and DuckDuckGo (browser) and both made my phone crashing when I had WIFI enabled - but in both cases it loaded page normally (which I had open from previous session) and only scrolling up/down page content made my device crashing.
After that I also tried HERE WeGo Maps and I downloaded some map content having only WIFI enabled and it seem to be ok.
when I try mentioned browsers without WIFI again, all works well..