"PowerPoint found a problem with content" - unable to Repair - I was in total panic mode...
I went through this last Friday night at 3am it was a total nightmare. Here's a fix... If you're on a Mac and encountering this error:
Open the file in Keynote. Save the file as a different name. Then send / save the file from Keynote as a PPT file with the new name.
This did the trick for me and fully recovered my PPT.
I hope this works for you.
Ryan
MacBook Pro 13″, macOS 10.13