@Christoph-Hart It was a dodgy faust node. I didn't bother to look at the faust code to see what was wrong. I was just going through the nodes one by one and deleting them and recompiling. I didn't need it any more and must have edited the code badly before going on holiday and forgot what I did. π
HISE was built with Faust and all paths set correctly to answer your question. Thanks for the help!