I updated both versions to 1.2.8. Please try to refresh the page or clear the browser cache.
It also often helps to remove and re-add a plugin in the plugin manager.
I cannot reproduce it, neither MV nor MZ, nor local nor web browser deployment. I wonder if it is an OS problem, as I only have Windows devices at home.
The last thing that comes to my mind is that when starting your game, you can press F12 to open the debug console, go to the "Console" tab, and check for error messages there.
When you feel comfortable, you can send me your project via [email protected]