Slideshow glitching from photos when exporting

I was having this same issue - Macbook Air M1, Big Sur. I tried exporting my slideshow several times and each time there were several glitches, just before a transition. It would play a frame of the upcoming picture, then go back to the picture it was on and then transition.

I tried creating a new library, exporting my images from my first Photos library and then imported them into the new library. The resulting exported slideshow still had glitches.

I went back to my original Photos library, exported the slideshow and did nothing else on my computer during export resulting in a glitch free slideshow.

Hi

Are you using the built in slideshow project? If so, you could:

Try a different theme

Try restarting your mac in safe mode and then trying, then restart normally and try again.

Try creating a new, empty library, export your slideshow images from your main library and import them to the new library then try the slideshow in the new library. (To create a new library, hold down the option key when starting photos. Same trick to choose which library to open)

If using third party slideshow module, contact the developers.

How much free space do you have on your boot drive?

How much memory does your MBA have?

As a test launch Photos with the Option key held down and create a new, test library.  Import some photos and test to see if the same problem persists. Does it? This tells us if the problem is limited to your current library or is more wide spread. Then open your original library and test again.