I use Chrome and have deleted the previous cookies that were stored for lemmy.world. After that, the login worked normally again.

delete your browser cache and try again. you should be able to login

Try these steps:

1. Logout via Home -> Hamburger menu -> accounts are at the top, click there and sign out. Try signing in, did you win?
2. If not, sign out again then long-press the app icon from your android launcher screen and select App Info, or find another way to get to the android settings screen for Jerboa and Clear Cache and Clear Storage. Try to log in again, did you win?
3. If not, sign out again and sign back in. Did you win?
4. If not, cry because I'm stumped. You could also try liftoff, which if you weren't logged in prior to yesterday shouldn't have a cached broken session. Or install the PWA from lemmy.world via Firefox mobile. Or use the brand new Voyager setup at m.lemmy.world again as a PWA via Firefox mobile. Of those, I like Jerboa and liftoff best.

Just had this issue, clearing cookies resolved it for me. Thanks everyone who posted the solution.

Finally able to log in again, thank you!