I can report something odd going on with SMS as well. My mother has an older iPhone 7, but running iOS 13. She can no longer (as of early February 2020) send or receive SMS text messages as part of a group. Individual SMS messages seem to work.
On my phone (iPhone 11) it works fine, but on my iMac (running Catalina) SMS messages are a mess. Existing threads only show partial messages, or show very old portions of a message. Again, the same thread on my iPhone is fine. Tried logging out and back into iCloud with no improvement. Restarted my devices...no luck.
iMessage seems to be working fine.