I read on reddit or xda that the problem could be with which android 9 ROM you used. Apparently, somewhere closer to android 10, a couple of the builds broke sms/mms on android for the 3A, which would break it here.
So, maybe try flashing an earlier or later version of the android 9 factory build. Could explain why some have working sms and some do not.
This is what I thought as well, On my 1st phone, I got sms working flawless by installing android 9.0 (PD2A.190115.029); I tried it on my 2nd phone and it didnt work.