First, let me say, I love this update to Start 11. I have relied on the ability to nest start menus and greatly appreciate this feature being added to Start11.
Now to comment on the reported issue. I have a similar if not identical configuration and if so, I think the report meant to say
"Occasionally I hit the start button and it's reverted to the Win11 start menu style . . ."
If so, I saw this myself just this morning and I can replicate it.
To pop-up a Windows11 style menu when Windows10 style is selected:
Move your mouse curser to "just outside" of the windows menu start button and click.
For reference I'm using a Win7 style start button with the start button moved to the left edge (not centered).
I can most reliably reproduce this problem with my mouse positioned diagonally from the upper right corner about 10 pixels or so.
Most people are likely accustomed to the entire start button area being the start button and clicking anywhere in the area. In this case I think the Start11 click area is slightly smaller than the area Windows itself has set allowing the mouse click message to be passed to Windows.
RE