Of course having the devs look at the scene is probably the best but I remember something like this happened for me in the past, too. Look out for some stuff in your scene and convert to mesh or hide and see if it is better:
- compound objects that may create notifications and trigger and re-parsing constantly - Scatterers, Booleans or 3rd party geometry and meshing plugins etc
- Body Objects that may recalculate tessellation if you use different setting for viewports and rendering
- ProOptimizer modifier, this one did a similar thing for me in the past
Try to isolate only a group of objects at at time, render, repeat until you find the offending objects.