Replying to a received group message was seen as a separated message on the receipents ..... on my S20+ with Android 10. On the separated group (bad) message, Selecting a message and view its details, you will see a From and Bcc...... and on the Good group message you will see From and To when viewing details..... this is an obvious software issue. For the time being, I am using Google Message until "Someone" fixes this issue. I am a bit upset with this $1000 phone. My old S7 with Android 8 has no issue with group messaging.
Hello I hope all is well. First things first does this group chat have members who are using iOS devices. Or non-samsung devices. I see you said you were switching messenger apps I personally use google messenger myself and it's a great app. If possible too I would recommend your carrier's specific messaging app