I've been reporting issue about font rendering in the past, recently someone else also reported something similar (can't find the post though)
I have this alias which draws an unicode character to a picture window, but sometimes it wasn't drawn correctly/entirely.
After a long debug, I've figured it out, it was whenever i joined a particular channel with a particular topic, which had a particular unicode character in the topic.
The first unicode character is drawn with "drawtext -rn @sbm 0 "Verdana" 14 770 400 $chr(9650)"
I'm realizing while writing this that verdana does not have the character, so font linking is occuring I suppose.
Once I join a channel with "PᗣᗧMᗣN" in its topic, the character drawn with drawtext is glitched, and this happens while the window is open with the correct drawing, I don't even need to close/reopen.
This is on windows 10 and mIRC 7.61, Wims, which helped with this cannot reproduce on windows 7.
I hope this helps resolving the various issue with font linking and font rendering, I can make a video if needed.