I bought a refurbished monitor online. It has weird spots - what is it (photos in post)?

Hi everyone,

I got a good deal on a used/refurbished Dell UltraSharp U3417W. Unfortunately after setting it up I noticed some weird spots on the panel which are barely visible on dark backgrounds, but pretty noticeable on bright backgrounds. They appear dark from lower viewing angles and bright from higher viewing angles. Here are two photos from different angles: https://imgur.com/a/ulIuohn

What is that and can I somehow get rid of it? I tried wiping them off but it does nothing.

Would appreciate any help! Thanks!