DRM? Maybe your tablet isn't fully supported for DRM by the app or your browser. The sound stream won't be encrypted so that's fine, and it's possible that some of the titles are held as a separate stream as well. Or maybe as stationary images they can be decrypted (more) successfully.
I've lost track of what Netflix does, but they've used and/or are using MS Playready, Widevine, and Playfair. They've been withdrawing support for older devices over the last 2-3 years, so maybe this is the issue.
If you're using the app, have you tried playing through Chrome or Firefox instead, and vice versa?
EDITED: 27 Jun 2021 10:56 by WILLIAMA