WIFI Calling Preferences Being Forced to Cellular Preferred

Same issue here. The problem seemed to first appear about 6 0r 8 months ago or so after an update. I then starting missing many texts and calls both coming and going…..very frustrating! My wife was having the same problem with her Note 8. As with others here, the T-Mobile coverage here is marginal and we depend on the WiFi calling for the majority of our communication…...not anymore! We were actually due for new phones anyway so I thought, rather than try to fix the problem, well, it must be our old phones. We upgraded to an S21 Ultra and a Note20 Ultra…..$2300 worth of new phones! Things seemed good for a week or so….then we seemed to be missing texts and calls! Our phones were again swapping to "cellular preferred"! This is completely unsatisfactory!!!!  8 years ago I swapped from Verizon to T-Mobile (even though the Verizon coverage was better) because I believed in the T-Mobile customer service and extra perks. But if the phones can't perform their basic functions, and, T-Mobile refuses to resolve this issue, it may very well be time to go back to Verizon!