YouTube downloading hundreds of files??!! [View all]

Hi, people. Sorry I only seem to speak when I need help, but I don't know what to do with this. My computer is everything - news, information, & entertainment - and I subscribe to YouTube Premium, which is well worth the price. Everything was fine until yesterday, when it became very sluggish, taking almost a full minute to load anything at all. Then this appeared in the lower lefthand corner:

https://imgur.com/a/H9mBlxD

I shut it down with difficulty, because the screen was nonresponsive at first, rebooted, and tried again. Same result. Each time, it shows a different number of files to be downloaded. The only way to stop it is to close the page, but it starts right up again once reopened. No other site is affected and everything else works just fine. I can't find any new downloads on my computer, as far as I know to check, so I have no idea what's going on.

Is this a fixable glitch or setting? Or is something more nefarious going on? What should I do now?

Also, YouTube is working and unaffected on my phone and tablet. This is only happening on my computer.