I just recently noticed that my TI-83 Plus, after exiting an application, begins throwing ERR:MEMORY and displays 0 bytes of RAM even though there was space before. WHAT THE HECK IS GOING ON!?

Please provide more helpful information. What is the application you were using? What did you do in it? Do you have other programs or applications installed? Maybe your RAM actually filled up due to unrelated reasons, maybe the application is trying to claim too much RAM, maybe it has a memory leak, maybe it doesn't deallocate an input buffer. There are many things it could be unless you are more specific.

I was running PuzzPack. I exited PuzzPack and noticed that running anything else would give ERR:MEMORY. Even hitting ENTER. Other apps installed are MirageOS, and Prob Sim. These other apps don't exhibit the same memory thing as PuzzPack.

Looks like the memory thing isn't happening anymore.

Then it was probably due to something unrelated.