technical difficulties and it's actively being restored. Check your "recently read" at the top next to the notifs and click ‘all’, or check your tags which can be found via your accountpage > Manga > column on the right. It gives you a pretty good view of your reads. all information on the issue can be found here: https://www.mangago.me/home/mangatopic/21080691/
Here is more info from Suujin
“The login info i meant is not the username and password. the issue is on the technical side of things like the login token. Even if youre only using two devices (or on your specific case, even if your logged in correctly), if that token gets corrupted, expired, or desynced from mangago's servers, the site can temporarily lose track of which manga and notifications belong to your account.“

I'm not getting the notifications.