@SilrFx Try to use google messages for the mean time just to see if the issue is the samsung app itself or the network. all text messages will be carried over to the new app there's no loss of any messages even if you delete google messages app after.
is it on AT&T and AT&T branded S10 phone? can you tell me more details?
@SilrFx when you open the group text does it prompt you it will be sent via MMS?
does this happened after an update? I have S10+ unlocked using boost mobile dont have problem with group text.
@SilrFx what baseband are you is it on ASD5? and ar eyou using stock samsung messages?