Labels not filtering

I had a few labels already, and they show up correctly, but when I click on a label it shows the “It’s empty here” view even though I confirmed in my Gmail that there are mails that show up with the label.
I didn’t file this under the bug filter, since I’m not sure if this is expected behavior. Do I have to reassign the labels to all mail that I had labeled before linking my account to 0?

Notes:
I made sure to select “All mail”.

Signed out, signed in again, the labels still don’t filter mail I labeled before linking to 0.
Tried both on Zen browser and Chromium.

Labeling new mails works as expected, and labels filter the mails I labeled with 0 and those I labeled on Gmail after linking my account to 0.