Problem after power cycle


I have working AB01 with distance sensor , all works good, measure distance for even week without a problem.My AB01 works on 3.6v battery.
My distance sensor is connected to vext …

But i want to debug it as much as possible. So i decided to keep removing battery and put it back again.

I noticed that sometimes my program does not want start, not sending join request , join accept.

I tried it on four - AB01 and tried different (same model) sensor. . Issue all the time is the same.

I did noticed issue when connected via USB

What could be the issue ? dont know what could be an issue really, please give me some hint