Probably because of the materials too, sometimes you have to change them to make them appear. Add a new Material Output. I had a problem like this where the materials were not behaving correctly because the output node from the 2.8 is different from the one used in 2.79.
Also look the Collections(new concept for layers) possibily some are not showing up. (although never had this problem)
With Eevee you don’t need to increase the Samples too much (since you don’t have fireflies), keep that in mind. I don’t know how much samples you set to render but if you gone high like cycles needs more than 100 you can turn this back down to like 32 and going up from there…
You can try the file I posted here BMW Test in Blender 2.8 - Cycles and Eevee
And test 32,100, 200, 300,1000 the difference is so subtle that you wonder if you need all the samples