Hi,
Well, it started when I received the new 5G SIM. Google Messages stopped working properly, so I uninstalled Google Messages and reverted to the stock Samsung/Android Messages App that came with the phones (mine and my wife's)
However, RCS messaging seems to fail a lot of the time, resulting in us having to wait for a spinning disc until it asked us to retry, which resulted in a few more minutes of a spinning disc, and eventually sending it via SMS.
It happens a lot with pictures so I end up getting charged the MMS message rate for each one when I intended to send it via RCS.
I do know a couple of people who have 'fixed' the problem by being sent replacement SIM cards...