My handmade fixed layout epub 3 is verified with epubcheck-4.0.1: no errors, no warnings. On ibooks and Readium: no problems at all.
I upload the file to my google play books library on Chrome, Firefox, safari. The epub doesn't open and gets stuck with "Processing..." keeping displayed after 10 minutes.
Now, I 'buy" a free fixed epub 3 from the google play books store. The epub opens. I delete the file from my library, download the epub, and upload it again. Now it doesn't open any more. Message: "This book cannot be opened This book contains content that is not yet supported in your browser."
I try the same procedure on an Android device. Same behavior.
I am stuck and would be grateful to have a few hints to move from this gridlock.