"Unsaved data may have been lost" and whole application got stuck

Creo has probably crashed. You can force Creo to quit by using the Windows task manager and killing the xtop.exe process in the process tab. If you lost some significant work because of this then you can edit the trail file from the session that just crashed and possibly replay the sequence to get the lost work back. Only attempt to use the trail file if you really understand what you are doing.

Save your work often because crashes do happen.

If saving is an issue because you may want to go back to a previous point in time.

This may already be known, but each save creates a new iteration and you can open them up if need be.

See below:

This may not help the crash, but you may not loose as much work.

Besides it is always easier to do the second time....   🙂

Often when I get this message, there is another little dialog box hiding behind that needs to be acknowledged before the OK button on this one can work...  It comes up if the connection to the server is interrupted, eg..

How to find these little windows?  Right click on the Windows start bar and click "Show windows side by side" 

Hi 

one of your user gets the error message : Unsaved data may have been lost

When you search the error message in the knowledge base you will find this article: https://www.ptc.com/en/support/article/cs34415 

Can you confirm that the message happens when coming back from Windows sleep?