Device 1: Razor phone 2, Android 9.0 with March 2020 security patch
Device 2: Samsung galaxy s20 plus, Android 10, March 2020 security patch.

Both devices exhibit the same behavior. Boinc continues to encounter an error and I get a popup telling me it keeps stopping. if I hit the back button, every once in a while I receive an error that there is another volunteer computing app installed on this device. Only one volunteering app can run at a time. I do not have anything else installed on either of these devices that is considered a volunteering computing program.

At this point, I think the Razor is crunching along, at least with the screen turned on. Both devices in theory have enough ram - 8 gb on both. I figure the Samsung in particular could get some decent (for Android at least) numbers in, but it doesn't look like it's even moving. Is Android 10 not supported?

Device 1: Razor phone 2, Android 9.0 with March 2020 security patch
Device 2: Samsung galaxy s20 plus, Android 10, March 2020 security patch.

Both devices exhibit the same behavior. Boinc continues to encounter an error and I get a popup telling me it keeps stopping. if I hit the back button, every once in a while I receive an error that there is another volunteer computing app installed on this device. Only one volunteering app can run at a time. I do not have anything else installed on either of these devices that is considered a volunteering computing program.

At this point, I think the Razor is crunching along, at least with the screen turned on. Both devices in theory have enough ram - 8 gb on both. I figure the Samsung in particular could get some decent (for Android at least) numbers in, but it doesn't look like it's even moving. Is Android 10 not supported?

I think Android 9 and above have the tendency to put apps to sleep for power-saving purposes, this may screw BOINC up.
Android 10 may be more aggressive about this than 9.
Try turning battery optimization off for BOINC, it may help.

I have a galaxy s20 and Oneplus 6t crunching away happily. Both running Android 10.
Now, to get a few other devices going. Are you running 7.16.5?

Would be useful to post such issues on BOINC own forums too, not just inside project forum (cause it's BOINC-wide issue, not this project issue).

Regarding "another app"- it founds remnants of own previously running process (some lock file for example or smth similar) and complains.
This behavior I see on all Android versions I used and on all phones. If prev instance terminated abnormaly or even just closed - new one has good chances to complain. But this issue is not show-stopping one, just relauch BOINC app - usually it helps, 1-2 attempts at most.

And regarding terminations - this much more serious issue.
After upgrading to 7.6.15 I lost one of my crunching hosts - Redmi Note 5 phone. It worked OK with prev version but after auto-update BOINC constantly crashes. I had no time to fix so phone currently lost for distributed computing.
More thorough testing required definitely before to force updates!