If it's only a problem with some transitions and not with all transitions then this leads me to believe that there must be an errant keyframe at the end of the transition that is causing the jump. Does the transition appear to be correct in the Boris FX timeline? Can you describe what the jump looks like? Are you using a Library Browser effect or building your own from scratch?
Yes, transition looks correct in the Borisfx timeline and yes, I'm using the library Browser effects not mine, here jump description: just transition ends the next frame don't match it's a very sligth missmatch betwen the end of transition and the next comming video frame.
So does this problem occur when you create a basic transition without using a template from the library? For instance, if you simply apply a 360 degree spin to a track inside of the Boris FX timeline does the transition appear to work or is there still a frame mismatch when you go back to the host timeline?