When an object that has an ISemanticVersion field is sent via Helper.Multiplayer.SendMessage, and the receiver deserializes the object (via ModMessageReceivedEventArgs' ReadAs method), the ISemanticVersion field is not set. This is surprising, because the same object can be written/read from the save game file correctly. (Although now that I think about it, it's not surprising at all since SemanticVersion doesn't have setters for its fields. The inconsistency is what's surprising.)

I didn't chase through the code far enough to see where you might be able to insert the same JSON converters into the networking code that are in the data serialization code, so if that's difficult or impossible then consider this a request to update the docs / wiki for clarification of which object types are / are not supported in sending network messages vs. saving data.

Fixed in develop for the upcoming SMAPI 3.8.2. Thanks for reporting it!