Powerpoint import failure problem

We have had one ongoing problem with Quelea, though I suspect it’s not actually a problem with Quelea as such but with Apple. Our pastor creates a Powerpoint each week on his Mac and sends it to me; I then have to adjust it in LibreOffice because Powerpoint on Mac seems to be a bit odd in its settings. I save the Powerpoint back as pptx, but it will never import into Quelea - the bar at the bottom keeps spinning and it never completes. The Powerpoint is small - a few K in size - and Powerpoints from other sources open just fine, so I’m interested also if you have come across this and have any suggestions?