I experience screen lockups and significant UI slowdowns on Linaro releases 20.02 and 20.07. I had no such issue when using release 19.01. The situation seems to be worse on 20.02 where the Xorg server halts and pressing Alt+F1 takes longer than 5 minutes to switch to the console and ten it takes several minutes to login in terminal. In release 20.07 I can see a similar issue, the lock-up is less severe, the screen usually unlocks within tens of seconds. Entering the terminal screen (Alt + F1) is quicker as well (several seconds). What I observe in terminal are kernel messages like this:
wcn36xx: ERROR hal_enter_bmps response failed err=1
wcn36xx: ERROR Can not enter BMPS!
msm_gem_shrinker_scan: 6 callbacks suppressed
Purging 16384 bytes
Purging 221184 bytes
I’ve done apt update and apt upgrade, the issue is still there.
The issue happens ~after 30 minutes of browsing the web while connected via internal Wifi. Please note that using Chromium web browser is problematic as well, there are some severe scrolling issues preventing comfortable browsing. I’ve installed Firefox and it works OK, but after browsing a while some news pages like bbc.co.uk (20 - 30 minutes) the lock-ups occur.
It does not seem to be related to heat, when touching the SOC metal shield it is warm, but not hot.
I’ve been using release 19.01 and I did not see such issues there. So far the solution for me is to use the 19.01 release.