I have the App Store version 1.2 and am unable to save files (Failed to save document: Save failed because you do not have permissions to create a file in that location.) I have repaired permissions, reset passwords, checked Finder-level info settings for all the directories and the desktop where I've tried to save multiple files, and each time I get the same error message, even after a clean install of new system software and re-downloading Affinity Designer from the App Store.
The beta I was using last month had no problem saving files, but the previous App Store version had this problem as I wrote to your tech support on February 20.
I hope you are able to fix this bug. I spoke to Apple Tech support yesterday and they told me it was a known problem on your end.
Best,
Clint