matterircd: Unable to /join a public channel or /part any channel from IRC

Hi,

When I try to join a specific public channel from my IRC client, I get this:

:matterircd 473 kotodama #whatever :Cannot join channel (+i)

Same if I try using ~ instead of #. When I join the same channel from WebUI, channel being public and not invite only, I properly get a:

:kotodama!xxxx@localhost JOIN #whatever

Also, when I /part a channel from my IRC client, it behaves as if I left the channel, but then I’m still on said channel when I connect to mattermost WebUI. This is the raw log from hexchat:

<<PART #whatever :Leaving
>> :kotodama!xxxx@localhost PART #whatever :Leaving
>> :matterircd 442 #whatever :You're not on that channel

Let me know if there’s anything I missed or if you need more details. Thank you!