Extruder clogs with HIPS
This has been sitting for a long time without an answer, so let me answer with an experience I've had with PETG rather than HIPS. 

PETG seems to be a relatively soft plastic.  It isn't soft like TPU, but it is softer than PLA or ABS.  The HIPS filament (which I have but haven't used) appears to also be softer, so it is possible that my PETG problem could relate to your HIPS problem.

I was printing and re-printing an object with PETG that had worked fine with PLA.  Three times in a row, I got a filament jam in about the same place.  

The problem was that the filament was retracting, returning, retracting, and returning many times within a very small amount of extruded plastic.  My extruder was set for high pressure between the drive roller and the idler.  When the filament went back and forth through the extruder, it flattened enough that it would jam from being too wide to fit through the next stage (in my case, a Bowden tube).

When I reduced the compression of the filament in the extruder, the problem stopped.  I also reduced the retraction distance, and increased the minimum travel before the slicer would do a retract.  Both were intended to reduce the number of times any single bit of filament would pass through the rollers.