I'm not sure how the tests wouldn't have caught this bug.
I have a .net class that has the function AddQuery with the following method signatures.

AddQuery
    Void AddQuery(api.QueryType)...
    Void AddQuery(System.Object)...

where QueryType is another custom object type.

On 2.0 and 2.1dev1 the function works as expected.

• I can pass a QueryType object to AddQuery and it would call the first method.
• Calling AddQuery with a string or int would use the second method and process them.

On 2.1.0 and the earliest archived copy in appveyor this behavior changed.

• Passing QueryType object to AddQuery still works.
• Passing string type to AddQuery errors with No method matches given arguments

I've tested on Python 2.7, Python 3.5 both x64.
Looks like Pythonnet is no longer identifying string int and other types to be of type System.Object as well.