There was no intentional blocking of Tor there in the past as far as I understand. But there are some mechanisms that block users from IP addresses that posted spam or abusive content. Those are automated and based on flags and not directed towards Tor specifically, but of course TOR addresses are more likely to have been misused that way so your chances of encountering these blocks is dramatically higher when using Tor. But these blocks only apply to low reputation users, I think once you're above 100 they don't matter anymore. And they also don't block reading the sites.
There have been DDoS attacks recently on Stack Overflow and Stack Exchange, I think it's quite plausible those have something to do with this. They still seem to be under active attack intermittently.
There have been DDoS attacks recently on Stack Overflow and Stack Exchange, I think it's quite plausible those have something to do with this. They still seem to be under active attack intermittently.