It’s an ad blocker blocker they’ve been implementing as of late. I don’t think you’ll be banned if you continue disregarding it, but they do eventually entirely block the video player unless you disable the ad blocker. However, in my experience, uBlock can block that message to resume normal watching. (Double Edit: This method did stop working on the 15/10/23, but started working again a day later. I guess it’s a question of if the filters have been updated to counter YouTube’s updates, though I did notice that viewing in a private tab worked when regular browsing didn’t.) Go to the extension’s settings/dashboard (on Firefox, do this by clicking on its icon in the top right, then the settings icon in the subsequent pop-up), then the Filter Lists, click “Purge all caches”, then “Update now”. Open an entirely new YouTube tab (or hard reload your current one by pressing Control + Shift + R), and the message should stop appearing, at least for the time being.