It's not terribly unusual for bugs to affect some people and not others, this is part of what can make them difficult to reproduce and track down.
What is clear is that for a lot of people neither of these increases happened at all:
And many people are running below their normal non-event averages for spawn totals.
I'm averaging a spawn of 7-10 collectibles each time, with a lot of 7s. This is on the low side of "normal" for me. I'm still closer to 100 at 63 than some people with more room.
I'm level 52.
My main island is not entirely cleared but again, my average spawn totals are on the low end of my "normal" average. Definitely not "more" in total spawn numbers nor pumpkins. I've blown up what I could and sent Gens to sit and twiddle on random Advs to clear space and seen no increase in numbers.
I'm on Sandycove. This issue has been reported in multiple fora, it's not confined to a single server nor language version.
I've now cleared the clouds from six archipelago sectors. The archipelago does seem to be having a more-than-random negative effect on things, somehow. Agreed it's not clear but it's worth looking at carefully.
I have a some Imp Storehouses, sometimes there are collectibles in them and sometimes not.
I have no paths.
The overall amounts of collectibles in the spawns seem more off than the pumpkins within those numbers, the range of individual pumpkin drops in the spawns seems more reasonable (purely from the "random" perspective) than the variations in the totals for "assorted" things.
While there may well be a bug tucked in some aspect of collectibles somewhere, and it certainly feels likely, there doesn't actually need to be a bug for the Achievement to be broken.
Goals with set time limits that rely on luck to complete them fail too many people too often to be viable here. This has been clear for years now.