I created a 4.5MB file on my Mac, and last time I accessed it on my iPhone and now I am unable to open it on the Mac with the error " The document “xxx” could not be opened.". I can still access the file on my iPhone and also shared it with an iPad, however I am no longer able to open it on the Mac.
I made a copy, and that did not work either. Thanks for help.
What is your version of the app on macOS compared to the one on your iPhone and iPad ?
They should be the same version to be compatible in both ways.