The Verge article:

“A significant number of subreddits shifting to private caused some expected stability issues, and we’ve been working on resolving the anticipated issue,” spokesperson Tim Rathschmidt tells The Verge.

So... According to Reddit the blackout is the culprit, I guess?

So either it's just an outage and they're faulting the blackout, or the blackout is actually the culprit. Either way I hope this works. However, I'm still not going back to Reddit even if they fix and reverse everything.

I wonder if it's bots or something trying to access the now dark subreddits. Essentially causing a DDOS.

well if i made a bot, hmm, yeah that could cause it lol. Like if i tell it "go in every 30 minutes & steal the top 20 posts", and it's down, i'd just say "retry till u get it, idc if u DoS that shit" and well if many ppl do it, it's a free DDoS courtesy of robotland