I had same audio issue with my Pro5 also. I think it's just another POS from china. Some phones are ok and some not.

My problem occurred in Android and UT/UB

This may come late, but deleted imeis can be restored quite simply in Android, hopefully in UB too in near future. I formatted them from my bq 4.5 an this is how i got them back. Should work with other phones too.

Open dialer and type: * #* #13646633#* #* (NO SPACE between * and #, This forum makes them italic if written together)
Click: Connectivity
Click: CDS Information
Click: Radio Information
Click: Phone 1
Type: AT +EGMR=1,7,"NEW IMEI1 HERE"
Click: SEND AT COMMAND
If OK was was reported, then go back and choose Phone 2 (If you have 2 sim phone)
Type: AT +EGMR=1,10,"NEW IMEI2 HERE"

After that reboot phone and sim should now work.

IMEI numbers can be checked with dialler command: *#06#

IMEI numbers can be found from sticker in phone or box or even from old phone. If imei from other phone is being used, then that phone should not be used at same time.

Looks like this annoying bug is still present. It's been since first release. Not sure about Ota2 i skipped that.