Handling time inconsistency

I've seen a few recent threads regarding handling time being set to automatic by Amazon without the seller's say so. It's happened to me before, and I turned it off. What I'm experiencing right now is something slightly different - my handling time is currently manually set to 2 days (since 7 days ago), but since then I'm receiving orders seemingly at random where I'm only being given 1 day to dispatch. I can't see any pattern to it -it's happening with Business and non-Business orders, Commercial and Residential address types, and no particular geographic patterns either.

Is anyone else experiencing the same issue? It's very frustrating.