I played through 1-133 and then 4521-4685 in a single session (with emulation pausing when I wasn't playing) before this occurred on 4686.
Next time I get around to playing, I could play in BGB instead of VBA and send you a savestate of the glitch having happened, would that help? I might also be able to savestate every level and get you a savestate just before the glitch. Just watch, in BGB the glitch won't happen.
If you'd like to send me a BGB savestate that would be useful for when I do try to hunt it down. Emulicious is also a useful emulator for seeing performance graphs. I would like to try to fix this bug and maybe add the random level option like you suggested, but time is a lot more limited for me lately. honestly I don't think I'll have much luck tracking down the bug even with a savestate of it. I'm not a pro when it comes to the Gameboy architecture/assembly so I don't have a super good understanding of how it's moving around the data. I do think using another emulator would be good though just to potentially rule out that. I only ever would play 100 or so levels in a session but it was typically on original hardware. It sounds like the issue happens after around 300 levels or so, so maybe I can build a test environment to just skip through 300 levels and see if anything is growing.
Also please redownload the game from itch.io just in case you're not using the most up to date one. I did one update around the time I submitted the game to fix a header issue with some flashcarts.
