I bought the proper oil for the damper service and used what I had for the lowers.
I have had all rebound go away on my pike – in fact Iv had no end of problems with it.
The first issue was I must have turned the compression damping nob too far (although this did not take a lot of force to do). This resulted in the compression nob no longer reaching an end stop and having no effect on compression damping (rebound still worked at this point). So I removed the blue compression top cap thing and started turning the shaft itself with a screwdriver (My original theory was the top cap was not mating with the shaft but this was incorrect). The shaft continued to turn without stopping and eventually became very loose and all rebound damping went away. When I opened the fork I found the charger damper in 2 pieces! So essentially if you continually turn the compression shaft the damper unscrews itself and falls apart….which is a bit crap in my opinion. anyway its easy to screw back together – I had to buy the bleed kit, reassembled, bled and all good.
2nd issue is I find the damping is good after a bleed but gets crap really quickly (but doesn’t go away entirely). There is a known issue for the charger damper seal head being rubbish, letting in air. So i just ordered and fitted a really expensive replacement from Australia. Yet to ride it and see if it works but the bleed seemed more consistent this time (more on this issue if you Google)
Essentially it sounds like for whatever reason your damper has failed – could be oil has leaked out – could be air has got in – could be something else (I have little confidence in these dampers now as you can imagine). But basically take it out and have a look.