Thank you, that worked.
Okay, so I did quite long debugging session, and the get_field() ACF api functions simply does not return the correct values as it should for some reason. I honestly don’t know why. I also tried different approaches, to get all the select elements and to find them that way, but they are simply not returned, only some of them. I googled around this issue, but there is no information about this whatsoever. Someone else had a similar issue mentioned on a stack overflow, but it was never resolved either.
I will try again tomorrow, but honestly this seems like some sort of ACF related issue as well.