I've experienced the phenomenon of the "disappearing shop" when my gut tells me that there's no way someone grabbed all of those all at once. Turns out some shops have a quota limit that we don't know about. So say there's a ton of opportunities in your area and you grab a good amount. You complete them and want to do more, but suddenly ALL of them are gone and you swear there were like 50-75 left. Turns out, if the company wants a sampling and the shoppers grab enough to make that sample, then all the shops disappear. Sometimes they reappear suddenly and disappear again, but you could basically count them gone in my opinion.
I saw this twice in my area. Once for gas station car counting opportunities and the other for checking stores for Samsung pay stickers. Both were insta-shops on the Presto map too.