After creating a support ticket, I got an email from support/Mindtree Limited/Microsoft suggesting to turn off "Explicit column selection" with no further details. This suggestions makes my PowerApp work and load properly, but after further questioning, if there were any other consequences, I just got a call with the content essentially being, that, one, Mindtree only had a bulletin suggesting that the turning off explicit column selection alleviated some (?) issues but no further documentation themselves, and that, two, I should post my issue in the forums, for the "team" (?) might see it. Hence, I have (re-)posted this message with a link to my original post and with a more catchy title.