[jpohlman]

Are you sure this is a seat belt monitor?
Have you checked the seat belt status screen?
The reason that I ask is that a Hybrid & PHEV use a CVT transmission which is driven by belts that move fore and aft on a cone rather than gear ratios being set by a bands and clutches.

 

[jpohlman]

LOL, ok then, the reason it's killing the cruise is because the Restraint Control Module can't read the belt status so it doesn't know which belts it has to pre-tension in a collision.
Try pulling the battery cable for ~35 minutes to force all the electronics to cold boot.