Many times I searched for 'how do I do something with xUnit' and found a github issue with people struggling with the same thing, and the author flat out refusing to incorporate the feature as it was against his principles.
Other times I found that I needed to do was override some core xUnit class so it would do the thing I wanted it to do - sounds complex, all right lets see the docs. Oh there are none, 'just read the source' according to the author.
Another thing that bit us in the ass is they refused to support .NET Standard, a common subset of .NET Framework and Core, making migration hell.