Question [Q] I9505 auto restore EFS after its delete, why?

I have Galaxy S4 (I9505) and after official update, I have faced error of unknown baseband and lost IMEI (null/null). Problem was, that IMEI and baseband were working only, when I fully discharged phone, put it on charger and turned it on. But when I called once, I have lost IMEI and basbend suddenly, same for the second start after 0% battery. I have made EFS backup via terminal emulator and "dd" operation - ( and to successfuly recover EFS, I had to delete it first. But when I delete EFS and reboot, EFS folder is not empty but is populated from somewhere. I am not able to get into "permanent safe mode" so I am unable to restore EFS.

Anyone faced the same problem? Do you know, from where is EFS folder auto-populated? I have also tried old stock ROM, problem is I cannot downgrade to original ROM before update, it was 4.2.2 and I can't downgrade bootloader. Newest 4.3 ROM also doesn't solve the problem.

Thank for any ideas