What exactly do you mean by “seasonal events”? Please give a few specific examples, including the event names, quests or duties, and the seasonal items you were able to get. I’d also like to know exactly how you used Welcome Vanellope with those events. Did you track an event quest and then enable the code? Which objective did it complete, and what became available afterward?
The code only force-completes certain objectives in the currently tracked mission: opening a specific menu, or submitting a DreamSnaps entry. It doesn’t directly unlock events, so I wasn’t aware it had ever affected seasonal content.
As far as I know, the limited-time features that actually require an online connection are Star Paths and DreamSnaps. Most other seasonal events can be accessed by changing the system date. However, if you already obtained their rewards with a GetAll code, the related event quests may no longer appear. Anyone who wants to play those events normally should avoid using GetAll codes too early.
I also checked R PickupToMax. It uses the game’s own stack limit and normal AddItem processing, so I don’t see an overflow or obvious problem in the code itself. DDV can lose sync between the inventory, UI, and field objects on Switch even without cheats, which can prevent picking up, dropping, or selling until the game is restarted. PickupToMax may make it happen sooner, but it doesn’t appear to directly corrupt the inventory.
