Animated GIF displaying correctly in PREVIEW + in Publish on Firefox, not on other browsers

Hello,

I've been trying many different ways, but I cannot seem to make this work :

I've produced an animated gif (display once, no loop), optimised via ezgif, imported into a storyline 360 slide ( 3.48.24159.0), exported as html.

I "reshaped" the image into a circle. (image shape > disc)

When opened in Firefox, the gif displays correctly.

When opened in any other browser (Chrome / Opera / Edge / iexplore) it just shows the first picture and then it's stuck.

Without reshaping the gif everything works fine on all browsers.

Any other settings (image quality 100% or less...) doesn't change anything.

I enclosed a stl file & export, on the right the "raw" gif that works, on the left the exact same but "reshaped" in a disc.

Thanks for your kind help!