All of the new forlorn snacks are able to have the auto consume option remain on but not actually consume the items. This happens from deaths and zoning that I can see. To fix this you have to turn off auto consume and turn it back on for the auto consume effect to work properly again.
This also happens for things like runspeed totems, actually. I spend too many rares on the snack scrolls to have them on autoconsume. I click them right before we pull a name. YMMV.
I have my scrolls on autoconsume and I agree with the OP. They will not always autoconsume. The Elixirs of Intellect also do not always autoconsume. Thorns seem to be working fine as far as I've seen. Please take a look at the autoconsume items in VoV. Something is definitely hanging them up.
this can happen for any autoconsumed item its just that the scrolls have a timer of 11 minutes so its more prone to happen