The TinySA app, with repeated scan off, makes a routine call to the TinySA for information (every 4 or 5 seconds) this includes the vbat data. I ran this for over one hour without any sign of failure. So I think the fault is not just vbat, but depends on other circumstances, maybe when the TinySA is very busy scanning and servicing comms there is an occasional glitch around the time of servicing the vbat routine

?