Why can't I open recent files in the Recent Files List?

Question

Windows

In Win10 v1903, I noticed that recent files that have a non-standard extension do not open.
For example, Notepad cannot open a recent *.md file , although *.txt files open fine.
The message " The selected item is not available. It may have been moved, renamed, or deleted. Do you want to remove it from this list? " appears,
although the file exists and is in the same place as it was.

My *.md files are assigned to Notepad.
They appear in the list of recent files.
But infections do not open.
In Win10 v1709 everything was OK.