From looking around those SanDisk forums I think your MP3 player is like many of these kinds of products. Pretty basic. BUT that is all you need really.
Kit like this doesn’t get much testing at the factory. Once they have something working it gets shipped. Then us geeks break it with our needs.
I would clear out the player, format, then start clean. Updating the firmware will help get you any bug fixes too.
Make a “MP3Player” folder on your PC. COPY your various albums to this folder. Use MP3TAG to strip the tags down to a more basic set. And set then in plain old ASCII (ISO 8859-1). Use Windows to set the ReadOnly tags. Now move these albums to the SanDisk player and see how they behave.
Why do I keep pointing to MP3TAG? Well, you can use that to set a different profile in there following this older standard. It is also easy to load up dozens of albums and then just delete whole chunks of data in one go. (For example - deleting ALL comments)
Also note how I am suggesting you keep your main library fully tagged up with Picard. And then make that temporary staging area to COPY albums to. That way you can downgrade the tagging for the albums as they get transferred to the player, but keep your main music library properly tagged.
Do a few experiments to see what your player likes the most.