Quassel IRC

I was connected to an IRC server.
Suddenly Quassel became super slow and i had high CPU usage.
Quassel became unusable and it freezes.
I killed Quassel using btop resource manager.
But when i run Quassel again, it's still unusable and it's frozen.
Quassel tray icon appears in KDE, but i cannot view the main window.
I had to uninstall Quassel, delete the config files, then reinstall it again.

Before Quassel freezes, i saw myself invited in many channels in the server i was connected to.
I think the admin attacked me using Mass Channel Invites, by forcing me into many channels, the UI had lots of processing and froze.
When i connect to the irc server via the browser, the admin does the same (or another, i am not sure) attack, i see lots of random ASCII characters filling my chat screen that freezes my browser tab.

How can i defend against these annoying spamming attacks ?

I am using Linux KDE Neon.