Unable to Undo and Redo - Lose ability to redo and undoing some changes

I have had an issue a few times now where I press undo a number of times to get back to a previous state and evaluate what the app looked like before I made some changes, but when I seek to redo those changes nothing happens. It's as if the whole undo / redo buffer has disaapeared which in some instances can result in the loss of an hour or so's work just because I wanted to review a past state. This is a new issue for me - I've not had this problem before the last couple of weeks so it seems like it may have been introduced in a recent update. I'm having a lot of stability issues with Dd at the moment which really frustrating and makes me want to start looking at alternatives. More than any new features I would just like to see the general stability improved.

Renamed By MOD