Problem with 'View in PowerPoint

I had a PowerPoint with some animations in the service this morning, so I knew I had to use the 'View with PowerPoint' option to show them. But it did not work properly:-
1) It did not start the first slide automatically, despite being set up to do so with the options.
2) The animations did not work anyway!
I had checked that the animations were properly set up by starting the presentation in native PowerPoint.
This was repeatable on two separate computers. Both are Windows 11, with all the latest fixes. PowerPoint is Office 365, again with all fixes installed. Presenter is the current build.
It is several months since I last used this option, but it worked properly when I did.
This feels like a bug. I hope it can be fixed quickly.