I'd call it a forum more than social media, the focus is on a topic rather than individuals. But when it comes to outages nothing beats Twitter. I'm not really a Twitter user, but when I click a link from elsewhere there's a >50% chance I'll get "we're having trouble loading this tweet".
Reddit started having a serious number of outages when they started rolling out their API-driven SPA-style frontend. Back when everything was server rendered it seemed far more reliable.