I'm getting this issue frequently... Video previsualisation doesn't run fluid when previsualising, which is normal as it's a previsualisation, but I don't understand why the same problem occurs in rendering. It even happens in the same frames. I know that Enscape uses GPU for rendering, but I think it is weird anyway.
PC is a i5-7600K with a Nvidia 1050ti and 32GB RAM. It happens in all Revit versions.