I'm using WIN10 Pro, TRS19 Build 116678 and this feature always works for me.  I, however, do not use notepad.   I use Visual Studio Code to edit TXT files.  It works every time (unless TRS19 fails to make the content editable).  I personally hate how wimpy notepad is. 
To make VSCODE work though, I needed to make sure that VSCODE was configured as the default editor for files ending in ".txt". (using OPEN WITH option and making it *default*)
Note: All my TRS19 content is on drive D in an unprotected folder.