I've been running LODA tasks on a Raspberry Pi 4B and finding that after appearing to run for a while, the computer becomes unresponsive. The display is frozen and there are no responses to the keyboard and mouse. The only alternative is to cycle power and start over. Sometimes the lockup happens within a few minutes, other times it's after a few hours. It only seems to happen when LODA tasks are being processed. Having the BOINC Manager running or not seems to make no difference. If no LODA tasks are executing, there is no problem. So it must be associated with the LODA tasks. Does anyone have an insight to what's going on? I've currently stopped all LODA processing.

That could be caused by memory shortage. Could you check how much memory you have available? You should reserve 1GB per LODA instance/task. You can also limit the number of parallel tasks in the project preferences if you have not enough memory available.

I've found that running 64-bit Linux/ARM tasks you'd best use Raspberry Pi 4B with at least 4GB of RAM -except for WEP-M+2 (Wanless) that needs far less RAM.
I frequently find out that my Odroid-N2+ (six-core Amlogic S922X) for some projects needs more than the 4GB that my version has.
And the same for a Rock Pi 4B (six-core RK3399) with 4GB of RAM.
As a rule of thumb my new ARM crunchers should have 2GB per core, just like my x86-64 machines used to have -I switched that requirement to 4GB more recently.