I have the Galaxy Note20 5G.
Both my parents have a version of the Galaxy S10. RCS messaging works perfectly fine with both of them. All 3 of us have Tmobile and are on the same plan.
My husband had the Galaxy Note 10 (or note 10 plus, cant remember). He was with tmobile on his own plan. RCS messaging working between me and him for a about a day or 2, then suddenly stopped. At the time that it did work and stopped, I had the Galaxy S10+. Then I got the Galaxy Note20 5G and it never worked.
My husband upgraded his phone to the Samsung Galaxy S21 Ultra 5G with ATT. RCS worked for a day and then suddenly stopped. RCS still works between him and his coworkers, but not between us. My RCS still works between me and my parents.
Any one else run into this issue before and know how to fix it. I don't like using google messaging and prefer to stick to Samsung messages.