That seems very annoying!
As this is a problem in the Mendix Studio Pro (desktop application), I don't think the community cannot really solve the underlying issue. If you have a small project, you could consider to file a ticket at Mendix support and send it along with how to reproduce this error. Only this screenshot doesn't help to understand what is going on exactly.
As work-around, you could try to copy parts of your existing page/microflow and paste it into a new document, this has helped me solve errors like these more than once.