On my S7 I have a high volume MMS group text with mixed devices (Droid/ iPhone) I encounter a number of issues when texts come in rapidly. The Message+ app would occasionally lock up so you could not send or receive. Uninstall reinstall fixes that but it became a hassle due to the time involved and the frequency with which it occurred.
Switching to Messages from Google and disabling Message+ seemed to work for a bit but I see the following now (with greater frequency)
It only happens with the one group, deleting the group does seem to make a difference, clearing cache didn't seem to help, rebooting either.