theres a big pause symbol in the middle of webms on e621.net now and it makes tracking really inconvenient for regular viewing.

have you tried to move your cursor off the video? because for me the pause symbol shows only when my cursor is on top of the video

e621 does not have its own webm player, we simply display the raw file and let your browser deal with it.

So, whatever happens is entirely on your end. You could try what Eggplant recommended, and failing that try out a different browser and see if the issue persists.

You could also try clearing your browser cache.

Firefox doesn't display the pause symbol, as example

If you're using chrome then you can disable the 'New Media Controls' flag by going to chrome://flags/#enable-modern-media-controls