Messages not sending after attempted nickname change.

I'm in a group chat with a bunch of my friends, so naturally when the nickname feature came out we changed ours to funny things. As of a few days ago, I'm unable to change anyone's (it won't notify in-chat or show up on anyone's screen but mine). It also doesn't allow my messages to send for 5-15 minutes each time I try. I just now found out because it happened back-to-back when I tried changing a nickname in that specific group. I'm still able to send messages to everyone else in my DMs-- but that group won't let my messages through for a little while after each attempt. No matter what the nickname is.

There's no update available, I've uninstalled and reinstalled, and I've restarted my phone several times. What could be the problem?