If I remember, we just added an LL_RCC_LSCO_Disable() with an angry comment in the RTC initialization code to reset the critical bits. Not the most satisfying solution, but we haven't seen the problem since
Thank you all for good advice,I'm fully aware about the uninitialized struct parts, but checking the code all relevant fields were initialized ok, so I guess we're happy with that.At least we found out (most likely) what is actually causing the probl...