For IRC rooms very often times, a single message is shown multiple times. Sometimes that can mean that the message is shown twice, or as shown in the screenshot, many times. It's very annoying because it makes the communication hard to follow and human unreadable.

Tested with Firefox IRC room using following room address: #firefox%irc.mozilla.org@irc.disroot.org

Reproduce should be as easy as joining that room and setting idle for a while, then looking at tghe messages. Allow a few messages to come in.

Happening on both iOS and macOS:
macOS 10.14.2, Monal 2.3 (110)
iOS 12.1.1, Monal 3.3