Milestone History deletes Undo History?

I just started using Cawemo.

I spent the day making a flowchart. I accidentally added a Create Pool/Participants, deleted it, which deleted my entire flowchart.

I clicked what I thought was the undo button in the upper right (Milestone History ) which seemed to delete the undo history. I googled it and found CTRL-Z, but this no longer works after opening Milestone History.

Is there some other way to undo?