Paul Goodyear

does the vertical smear change direction when you rotate the rangefinder?  
look for any 85mm/2.8 lens.  as a rule most 85mm f2.8 lenses are superb quality.  The jupiter is the best bang for buck,  closing to f2.8 and its a good choice.  if budget allows...  a 85mm/2 olympus zuiko is a nice lens
 

If you want to try something akward but which could give you the best quality possible, find a bronica nikkor-p 80 2.8, the back diameter of your sankor should match the front lens exactly. This lens has no helicoid and there are no adapters available, but since you have the rangefinder you could find some hardcore hot glue solution (gluing some extension tube to the lens).

I just got a set of old Russian nuclear lenses for this exact reason.
You can actually find them NEW on ebay because millions were made, and for 30-50 £
The only downside is I've grown a few extra fingers, but it makes focus pulling easier.

Anamorphic lenses actually work better when used with older, simpler, smaller optics. It sounds counter-intuitive, but the bigger and shinier the prime lens is, the crapper the anamorphic generally looks. This is why you don't see many people screw a Kowa to, say, a Canon L-series. It would look abysmal. This is why your 50 and your 135 look good, they are old, crappy lenses, whereas the Rokinon is a brand new lens, with a much larger optic.
 
My advice is to get a vintage 85mm. Something tiny, and preferably radioactive. It'll make your anamorphic sing.

I think it's "saggital coma" which an artefact in some lenses when used at their widest, though I could be mistaken.
if you don't like it you'll have to only use the 85 closed down, or find another 85 that doesn't exhibit this with your particular anamorphic lens.
or use it intentionally as a kind of romantic softening for portraits