Flatten Command only works occasionally in 2022

[ovenegas6BFTN]

AutoCAD 2022:  The Flatten command, both typed and also from the pulldown menus of the Express Tools, works on some drawings and do not work on others.  Right now I have one drawing open that when I use it, and I pull down the Express Flatten from the Express  tools, it tells me that "Flatten Unknown command "FLATTEN" ', but this morning, I was able to use it on another drawing on the same computer and used it to fillet lines.  Now I cannot use it.

Is this a bug with the AutoCAD 2022?

Please advise.

***THE POST TITLE HAS BEEN EDITED FOR CLARITY***

[pendean]

that just simply means you have that command unloaded for some reason like an add-on active in one workspace but not another, using LT accidentally and not full AutoCAD, jumping between AutoCAD profiles or variants where some have ET installed and others do not, or... .