Basically, I keep having to put the same straws for sale in store because they keep randomly being removed from store. I noticed this a few times throughout these last couple months specifically.

How long were they up for? From the game guide :

Straws not sold within 7 days will be taken down from sale by the game.

So you have to keep putting them back up

oh this could totally be it. Sorry, I didn't realize this was a feature!