8.5.20 - Undo/Edit MIDI disabled after recording

Sometimes, after I’m done recording on an instrument track, Undo will do nothing and the MIDI parts are untouchable. I can’t select them, can’t delete, can’t open to edit in the editor. I have to close Cubase and open again.

This only started happening once I updated to version 8.5.20. Anyone else having this issue?