Thanks for the suggestions. I’m still no further forward. I’ve tried an update of VS2017 to see if that works.
I’m starting to suspect the issue isn’t with MonoGame but the SpriterDotNet Importer itself. I cloned the repo (https://github.com/loodakrawa/SpriterDotNet) and while it builds, it still states in the content project that the scml files have an unknown importer, though correctly knows they use the pass through processor (No Processing Required). The XNB is correctly generated too with the initial header “XNBd »Á SpriterDotNet.MonoGame.Content.SpriterTypeReader, SpriterDotNet.MonoGame, Version=1.6.1.0, Culture=neutral, PublicKeyToken=null §‚<?xml version="1.0" encoding="UTF-8"?>
<spriter_data scml_version=“1.0” generator=“BrashMonkey Spriter” generator_version=“b5.95”>” followed by the xml files.
The project builds all the content and runs without issue. I may have better luck asking the maker of the importer.