Newly-bought battery for OnePlus 5T does not charge anymore

Hey there,

I've recently bought a replacement battery for my 5T.
The replacement process went well, and all worked fine(for a bit).

On the packaging(and here) it says to charge the battery to 100% and keep charging it(which I did), let it drain completely, and then charge it back up.
Now, I did the charge up to 100% + the extra 2 hours yesterday, where everything worked fine.
I let it drain over the course of today, and plugged it in when the phone shut down, just as described.
Since then, it hasn't been charging, and keeps showing the screen described in this post, which incidentally was the very reason I bought this replacement.

What's happening? I'm confused, the charging worked just fine yesterday, so the charging plug shouldn't be the problem. Did I just get unlucky and receive a broken battery?

Thank you very much for any help/suggestions!