I haven’t seen this bug for years but it’s back (for me, at least).
At some point during a max session my undo function will simply stop working. Ctrl-z doesn’t do anything, nor does the button on the main toolbar. If I right click this button there are no operations registered in the drop-down list.
Anyone seen this lately?
I also have this once in a while (in every Max version, still using 2022 though), it depends which action I did before, or which script I ran. I guess some scripts clear the undo buffer or something. It’s quite annoying.
In my current case it ceases to register any new operations in the undo list too. Very very annoying…
Well that is rather spooky…I read this post and was thinking I can’t recall that happening any time recently…and as if Max heard me it started happening just now 
For me it is Ralclone which initiatiated the behaviour. No doubt about it, as I have only simple other geometry and it directly occurred whilst tweaking settings in a new clone.
Reloading seems to reset it for at least a while.
Well I just had it because I saved…
Are you using Project Manager too by any chance?
Nope…basically vanilla Max with Fp, Rc…a few very minor scripts and that’s all.
I’ll see if it occurs again tomorrow…maybe it’s just because it knows we’re talking about it.
Generally Max does weird shit just when you think you have everything nicely sorted…
Often, MAX crashes on undo.
Ok. I have RC and FP installed too but I wonder even that is enough to cause problems (ie. not even using them, just having them installed).