Phpbb version 3.2.9
I converted from 3.2.3 to 3.2.9 some time ago, I cannot update it to 3.3.x due to extensions that I need, so I dont even try that with me.
When I try to go to the installed forum styles I've got error "NO_STYLE_CFG". But that file is present.
Sorry for an alarm.
I was thinking that old styles were deleted long time ago, but I checked sql tables for forum styles and there was my olf stuff counted as installed. So, my entire problem was few missing files that I forgot about because I dont use them for years.