I'm not sure why "ircii" won't work, but "irssi" works beatifully! I couldn't even get ircii to work on my mac mini running minicom version 2.9 connected to my WiFi RETROMODEM V3 - same thing, the cursor just goes up/down one line in the top left of screen endlessly. But "irssi" works on whatever environment I've tried so far!
Below is "irssi" running on both my IIGS via ANSIterm and my C128 running DesTerm
On my IIGS I have a WiFi RETROMODEM V3 that I use to connect to Raspberry Pi where "irssi" is being run.
On my C128 I have a Link232-Wifi cartridge, which is a combination Swiftlink cartridge and WiFi modem. I then "dial" into the Pi same as IIGS.
Both modems use variants of the Zimodem firmware.
Back in the day I primarily used my C128 as a terminal to dial into a local Freenet system, an m88k machine running SysV, and some Ultrix hosts I had access to . From there I could explore the early internet! A lot of time spent on email, IRC, gopher, MUDs, Usenet all from my C128.