it happens to me too. I can't figure it out why it happens. Sometimes I think it is because of the video encoder setting. Made dozens of tests. No solutions. Keep going on in the darkness...
i MAY have found a possible workaround - it seems to work fine for me:
I ran some auditing on the page i created with edge animate - it was telling me that there was no cache-expiration set for any elements and that some browsers might not cache elements if that is the case. Caching seemed crucial to me for the preloading process, so i then set up an .htaccess file in the folder on my server and added the following content:
ExpiresDefault "access plus 1 month"
ExpiresByType image/x-ico "access plus 1 year"
ExpiresByType image/jpg "access plus 14 days"
ExpiresByType image/jpeg "access plus 14 days"
ExpiresByType image/gif "access plus 14 days"
ExpiresByType image/png "access plus 14 days"
ExpiresByType text/css "access plus 14 days"
ExpiresByType video/mp4 "access plus 14 days"
the last line was the most important one in my case, since i have much .mp4 content - everything else need to be adapted to your needs.
Since i added this .htaccess file, everything works as expected.
However, this doesn't have to be a workaround for all cases..
Maybe you can try it and see if it works?