Updating cover art for custom playlists on macOS or iOS

I have A LOT of custom playlists, and most have custom cover art that I upload and attach to the playlist. Every once in a while, I have a hard time getting Apple Music on macOS to accept my custom cover art — instead keeping the default cover art or one of the built-in ones. I can usually get Apple Music to accept my custom cover art by doing some combination of...

• Switching to one of the built-in cover art options and then trying to re-upload mine.
• Reducing the size of the custom cover art I am trying to upload
• Log out and log back into Apple Music.
• Try creating a newer version of my custom cover art and/or change the file format to another supported one.

However, in the last couple of days, nothing has worked, and I have been unable to add custom cover art to my newer playlists. Switching to one of the built-in cover art images works every time — it is only when trying to add some custom cover art that it ignores what I am trying to do and keeps whatever cover art is currently configured.

It also does the same thing on iOS 18.2.1 on my iPhone 14 Pro Max

Anyone else run into this or have any other suggestions I can try? Is there a limit to how much custom cover art one can use?