From what I've gathered so far

I've been going through old accounts, specifically accounts made in early 2016, 2015, & 2014 and they're slowly getting their "Already read" list updated and restored. Some have 1000+ recovered, even the inactive accounts. It's probably being recovered from older users to newer users. It's gonna take a while, maybe even days or weeks, but it's slowly being fixed. I feel like the influx of comments right now is making the site lag along with the data recovery. For now, just pick a story and read that while you wait for your list to recover.