I am using the NotePro with Android 9, version 2021-08-10-27_3.1_959a7b5. So some flavor of 3.1 from the middle of August '21. However, I can't update yet to 3.2.
Since when could you update to 3.2 on Android 6?
Normally, I would go over
the common points first. Especially, disabled system apps, such as Google services.
However, cleaning the cache and data of an offending app and even reinstalling that app, goes a long way to getting rid of random reboots. I remember this being repeatedly necessary for my old LG mobile, when LineageOS had another system update.