GTP 8.4 CM12.1 not stable

Hi,

i have been using latest CM12.1 nightly but my tablet is stable even for normal usage.
1. some of the notification tiles are not working like battery performance mode etc.
2. tablet restarts by itself after inserting sd card or pendrive.
3. Tablet reboots after changing CPU governor.

recovery : TWRP 2.8.6.0

Flash method: Clean install always. no OTA update
what might be the problem?
Now i have switched back to stock TW ROM.