This happened to me 5 years ago and I thought I had to make a new account. My laptop broke and I tried to log in though my phone, it didn't work, made a new account, and a few years later I somehow logged back in. I think it's because I didn't have the same account on my browser. I was logged in on chrome on my laptop, but was using a different account in my phone's chrome. Save your mangago acc and password to the password manager for autofill, log on the same browser account on your phone and turn on autofill, then try to log onto mangago. I hope it works for you.. if not, I can try to juggle my memory a bit more to pinpoint the actual method.

Okay, I almost had a heart attack!
I am still unable to log in from my phone, don't know why...But I somehow could log in from my laptop and luckily all my list are still there
Maybe it's a bug they're still solving ╥﹏╥