Such an issue could occur due to serval issues, do you see the fallback image instead of the video on mobile?
Please try these methods and tell us if they helped:
Regenerate the CSS via Elementor > Tools > Regenerate CSS on your WordPress Dashboard.
Go to Elementor > Settings on your WordPress dashboard.
Click the Advanced tab and then switch the CSS print method to Internal embedding.
Clear all cache: your browser’s cache, other plugins’ cache, server cache (if possible).
Go to Elementor > tools and enable the safe mode setting there.
“Safe Mode” is a safe environment that isolates Elementor and WordPress from all themes and plugins, it helps multiple users solve issues like this. If it helps, Deactivate your plugins one by one until you find the culprit.
If it deactivating plugins doesn’t help, switch your theme (temporarily) to a default WordPress theme such as Twenty Twenty One and see if it makes any difference.
Switch the CSS print method back after following these steps, regardless if it helped or not.
Those steps cover the majority of probable causes, hope it helps.
