Best bet is to remove the save file or find a way to dump it to a PC and remove whatever was traded. I assume that would fix the portion it's calling on causing corruption. Sadly odds are file is lost at this point and will need to start from scratch. If old enough battery will need a replacement for save file longevity regardless.

I would give a shot at cleaning the Dpad registers, you could have some gunk causing "drift" as they are connected input wise. And if that's the case the issue was never your stick to start with.

Might need to provide additional information here. Does this happen with GBA games or GB(GBC) games only? A specific game or all types across the board? I know the issue can span from dirty pins and cold solder joints on either system mobo or game cart pcb. Console mobo being the harder repair as you have to trace back and find where the issue is. Currently working on this on a unit myself and occurs only with GBA carts. Calls for the info after Nintendo Logo and stuck on the white screen, doesn't boot the game (which works on plenty of other consoles).