I've had this issue when I have too many tabs for this site open. I suspect, but haven't checked, that leftypol runs some kind of service worker or something that just falls apart when running for a long time with too many tabs open. I used to have a similar issue with running regular Twitter and browsing through too much, it would just crash after a while and start working again.
I'm also running windows and also suspect it doesn't deal with it well either. I'm switching to linux soon and should be able to compare then.