Motorola Moto G — Problem with MMS on wifi and data saver

I just acquired an unlocked AT&T G6 play on ebay. Phone is like new and very nice, seems to be completely factory reset, etc. All is working well fine on my network (US Mobile) with APN set up properly, etc. except 1 big problem. I cannot send/receive MMS only with this specific condition (took me a a while to diagnose):

Both wifi is on (of course network data is also on and datasaver is on.

Network data is also on, of course, I know I need that for MMS even if wifi is enabled... this is not new to me, just to this phone...

I just upgraded form an e4 that broke and also have a g4 and have no problem sending/receiving MMS on either of those with both datasaver and wifi on. I have a low data plan so need datasaver, and I also use wifi at home all the time. So this is a major headache that mms incoming hang (i get the text but stuck on "downloading...") until I either turn off the wifi or the datasaver manually... does anyone else with MMS on G6 Play use databaser and wifi ? It is not a rare combination to avoid background downloads for application updates, other stuff, etc. I tried adding more background apps and some additional android services being turned on in datasaver (messaging app IS on), but it did not help. It works fine with data saver OR wifi, but mms both inbound and outbound get stuck when both datasaver and wifi are on. Very frustrating... thanks for any help.