I opened a file created with Affinity Designer 1 with the new Designer 2.
I saved it with a new name, edited the file for more than 1 hour, saving it many times.
At certain point I opened Affinity Photo to edit a image to insert on Designer.
Some time after that, after insert that raster image, I tried to save the Designer file and a box was presented saying something like: "Failed to save Document".
After that point, the icon for the file changed to a generic Affinity Designer icon and became impossible to "save", "save as" or "open" the file.
My only option was look for the previous version at my Time Machine Drive.
I opened that file, imported the raster image again and finished that job. I'm reporting just to leave a record in the case that more people find the same problem.