For me, twitter regularly starts behaving bizarrely. Tweets pop in and out, or change order while scrolling down the list. Happens in Firefox 70, with addons both enabled and disabled. It's quite annoying, and when it happens it'll stop loading tweets after a while.
Also if you scroll long enough (and sometimes not that long enough), it'll stop loading new tweets.
It's likely the out of order tweet loading makes it go wild.