I observed this many times already on different smartphones:

BOINC stops computation. And the reason looks like: Battery charge 100%, computations will be resumed when battery charge reachs XX% (where XX is value set in options for particular device).
So, BOINC can't understand that 100% > XX% ?
Usually after ~minute it realizes that 100% is enough and restart tasks.
But when I take phone to discover such state it is cold. So, computations weren't done long time already before this check. And only bringing BOINC foreground (and awaiting ~min or so when it does right math) resumes computations.
Quite big inefficiency buried here.

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Had the same on mine.
Occasionally, Android freezes. It's not meant to run 24/7/365.
But setting minimum battery to 0% solved it for me.
My one phone is plugged in 24/7. The other nearly always (office, car, bedroom, even when I'm on the couch).
Occasionally it still stops, but not due to a battery issue.

Unfortunately it's my main phone currently so have it unplugged quite often. And battery drains too fast with BOINC. So had to increase limit to ~80%.
From the other side, I still want to use battery enabled for computations not to stop them on short re-connection to power source.
There are computation errors on rosetta for example due to big number of restarts. Hence the less pauses will be the better. Allowing battery for computation for some % reduces number of restarts.

So, the best option will be to get BOINC compare current charge level with allowed one correctly to use this option as it intended to be used.

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And even more unfortunately: when I removed battery from power sources BOINC started to suspend computation for another reason - not plugged to power source (being plugged with 100% batery charge btw).
So, here is big issue with proper power detection in BOINC for Android.
For example, last night was completely lost again - device didn't compute though I leaved BOINC as foreground process and phone plugged before sleep. It just lost understanding of being plugged somewhere through night (it computed OK when I leaved it).

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The Android client for BOINC is being rewritten from the ground up, so reporting any issues with 7.4.53 or 7.16.x (whichever works for people) is fine with me, but it won't be acted upon because the old clients are going away.

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Too many people mentioned battery issues when trying to crunch on a phone.
Batteries heat up, and blow up.
On my essential phone, there's a neodymium magnet at the point where an external camera can be mounted. It's very near to the processing core.

It's so strong, that I can stick my phone on any metal surface (save for a perfectly flat vertical surface, where it'll slide off).
So I put it on a metal table next to my bed at night.
The magnetic pull on the case, forcing the phone on the metal, somehow draw out all the heat.
The phone doesn't even get warm in this position.
So far I've been crunching on it for almost 6 months, and no battery issues yet!
I'm very surprised it's actually a phone that's just as good as a Pixel phone, or IPhone of that time!

But many people run their phones in a case.
Many people mentioned their screens popping out, the back of their phones bulging.
Personally, i wouldn't crunch on battery; and unless you use your phone without a case, don't crunch at all; unless it's an older (backup) phone that doesn't matter much to you.