Only *some* of my custom cover arts are working

[tosubks]

Plan

Premium

Country

USA

Device

HP Envy

Operating System

Windows 10

My Question or Issue

I tried doing the trick where you put album covers on iTunes songs then transfer them to Spotify, but it turns out, only a few of the songs actually had their cover art transferred over. The rest are just the default gray music note. Pretty confused.

One of the pictures that worked was 674x674, and one that didn't work was also 674x674, which makes me think size wasn't the issue. They were all done in a 10 minute span. 

Thanks