Defnitely check if you need wheel axle spacers to align the rear sprocket with the front. There's no reason the chain should jump with less than an inch of slack, unless the in-line sprocket alignment is way, way out.
If it is, then the sprockets are likely worn on the edge(s) and the chain will jump. From the back, look for points instead of square teeth.
Replace sprockets, chain, and get spacers as needed. No more problems!
And Blair at SVRacing can help you in all aspects.
DonStrom6 - PHL
DL1000K5 - Black and a Blast!
DL650K8 - Yellow Sold