NormanTaylor

I have exactly the same problem. I am using Windows 10 on a Surface laptop and after several hours of editing a previously saved file, I attempted to save the work. The message reported that it is unable to save the file due to an internal error and advises to contact the Development Team! Neither Save nor Save as works, but I could export to .pdf (although this only served to remind of the time wasted getting there.) The problem exists whether saving to the onboard memory or to an external SSD. File Explorer shows the 'saved' file with 0 content and, not surprisingly, this opens with a message the the .afpub file type is not supported.
This is not just an irritating glitsch - it means that the programme is unusable, even though work must go on. We need an urgent fix, please.

Thank you, Alfred, for this prompt response. It is reassuring that I have stumbled on the best way of dealing with the problem. I should have liked, though, to be able to check progress without having to go out of Publisher and save to .pdf every time. But so be it!
I know absolutely nothing about 'font metrics', but suppose that, in this case, it boils down to what the software expects in terms of y-axis dimension of a descender related to the x-axis, for any given point size. I could understand the software setting limits on this and ignoring values outside the expected range. This is apparently not what  happens though. Publisher retains the out-of-range data and only abandons it in the print routine. The original data is preserved throughout processing and it can be accessed in the .pdf in the desired form. It would be nice if Publisher, like Photoshop, allowed printing, in the native programme, of the data which it has held on to.
Thank you again.