198/199 sidequests done and a single Jumbo Pumpkaboo is standing between me and 100%

I'm at 198 of the 199 sidequests in Legends Z-A. The only one left is the quest that asks for a Jumbo variety Pumpkaboo.

I've been catching literally every Pumpkaboo I run into — not checking, not skipping, just catching all of them — and it's been several days now with nothing. At this point I'm starting to wonder if I'm looking in the wrong spot or if there's some trigger I'm missing.

Anyone know if certain areas or times have better odds for the Jumbo size? Or is it purely down to luck and I just need to keep grinding?

Any tip is appreciated. This one quest is the only thing left on my file.