Slow and unresponsive group chat on iPhone

I have an issue accessing and sending messages within one of my group chats. When I open the group chat the app becomes very slow and unresponsive. It won't register any of my presses or swipes and appears to be lagging out. I don't have this issue with any other group chats on my device. I'm not sure if this is an issue with my device or one of the other users in the group chat.

[Re-Titled by Moderator]

Original Title: Can't Access Groupchat