I did two things that seems to have (at least on a limited run) fixed the cellar detection issues I was having. (Note, I am running on all low settings and was still having cellar detect issues on the latest).
1 - took my own SS and cropped the cellar png so there was no surrounding pixels - not sure if that makes a difference, but as the terrain can be obscured sometimes on the map, figured why not.
2 - I had my wormhole delay pretty low because it was working fine with getting the next casts off (using a 1.59 spd 1h with less than 200 abort spell delay). However, it looked like sometimes the minimap update lagged just slightly after wormhole finished - 1 guess was that it wasn't on-screen in time for the cellar detect to go off. I haven't looked at the script in the latest iteration, so I'm not sure if cellar check time will accomplish the same thing (I'd assume it would, but who knows).
edit: Looks like chancity said the same thing (+ extra wisdom) a minute sooner than me. --@Chancity, major props to a fantastic script btw!