Hello,
thank you for your purchase and sorry for the issue you are facing.
What kind of shutdown ? It automatically reboots ? Or it really shutdowns and you have to long press on the power button to turn it on ?
You can try to use your FP3+ in Safe Mode for a few hours in order to see if the shutdown still occurs.
It would be interesting to have a bug report please. You can see how to generate a bug report in this HOWTO (it shows Android 8 and you are on Android 10 so some paths might be slightly different).
Then you can upload the generated zip file here, I will submit it to the team.
If you don’t feel comfortable in doing so, just don’t do it, it’s not an obligation.
Have a nice day !