I've received my car back from the service today. Backup camera was one of the issues I've mentioned them. To solve the problem they have updated the ISTA (I-STEP?) version.
I've attached official BMW problem solution documents. Oldest one is about the all cameras and suggest to update ISTA to S15A-17-11-520 or newer version.
After that there is one more which refers to a green bar on the screen when reverse gear has been engaged (update ISTA to S15A-17-11-541 or newer version).
Latest one is directly related with the backup camera turn-on issues; and suggests to update ISTA to S15A-19-07-553 or newer version.
Mine was S15A-17-11-540 which had a backup camera issue. According to latest document problem should be solved now since it was updated to S15A-19-11-534 which is the latest version as of today
I hope this would help people who has the same issues. I'll wait and see if this really solved the problem
Cheers,