Hello!! If it makes u feel any bit better, this is an experience everybody on the site is going through right now. Yesterday, I had read on here, took a break, then around I believe 11:30am last night did I notice all of my readings were gone as well. So its been a hot minute that this has been ongoing, but according to some users, the lists will slowly be coming back! I would advise you to not edit them currently so it doesn't mess with them making a comeback for you (which is why I created a list that ill add them to my readings when they come back)
But yes, I'm sorry for all of us ( ̄ε(# ̄)Σ Give it some time, I would suggest! This website encounters issues all the time, but the dev's wont let issues sit around
My history of what i read is still in the manago history and in my browser history, I'm using they to retrace my reading. Also, you're"reading" items that got notifications are still up so you can find those there.
Honestly I've been finding my reading lists that way and re-adding them. I'm still on the verge of crying, but I'm holding onto a sliver of hope that everything gets fixed

this morning I realize that all of my manga that were "read" were not on my page anymore. but what annoys me the most is the fact that all my manga that were on my "want to read" list disappeared too !! what can I do ?? I read like a 1000 mangas and I like to keep up with them (what's surprising is that my rating is still there just the manga is not on my "read" page). I don't know if I was clear but I'm so fucking sad !! how can I fix this ???