I did some digging into this today. I didn't see the issue on my system either, but I noticed I am up to date with all of the commits on master (QtPlasmaC version 008.048), whereas you are on 008.043. That is from May 4, 2024. I did some digging in to the commit history, as I vaguely remembered seeing something involving Motion, and I found this commit:
github.com/LinuxCNC/linuxcnc/commit/6598...13e27e03e792dc838c86
in the commit description, it solves some M67 issues. Here is the issue it claims to have fixed:
github.com/LinuxCNC/linuxcnc/issues/2987
At any rate, I checked out the commit before this one (469ab15), and recompiled the project, and I see similar issues to what you are seeing. M67 does not seem to be effective. I think I can safely say this is the culprit. It does beg the question as to how long it was broken, but nonetheless it seems to work again.
Long story short: You need to update.
Happy cutting.