Actually that's the difference that matters. MUI after 3.8 requires more stack (don't know why). I've seen this with Poseidon but not with AmIRC. One alternative is downgrade to MUI 3.8, the other possibility is to use one of those programs that help you force the stack to a minimum size (StackAttack, MinStack). One of them is mentioned here:
https://forum.amiga.org/index.php?topic=70206.0, the other one here:
https://forum.icomp.de/index.php?thread/1230-psdstackloader-stack-problem-with-mui5/&postID=9939I think in the end what you are seeing is because of MUI, not AmIRC (or not *just* AmIRC at least).
Personally, I went back to MUI 3.8 and both Poseidon and AmIRC are happy on my system.
Hope this helps
Regards,
Efren