with the update from 5.3.1 to 5.3.2 you changed the way to include the pro fields (repeater, flex, …).
I developed own fields based on your great flex and repeater field. All my fields are based inside my theme folder and i just include them. it is important, that the original pro fields are initialized before i include my own fields, cause i youse the original classes for my own fields.
with 5.3.2 it seems, that the intializing of the pro fields has changed! the fields/classes are not initialized before i include my own fields.
//ONLY adding these three lines of your acf-pro.php helps at the moment
//now i am including my own fields