Balazs Hideghety at Ceremity/UPS didn't want to use the Core First version of Entity Framework with .NET Core.

I always assumed that he didn't know what he was talking about, (He disliked and didn't use interfaces in C# and thought that microservices and domain-driven design were synonymous.) but since then I have run into others echoing the notion that the first rollout of Code First Entity Framework for .NET Core was pretty bad. I can't tell you what was so terrible offhand, but apparently as of .NET Core 2.2 it is solid and shipshape.