This is a design engineering issue. If this issue results in a placard having to be fitted to forbid or limit operation in a specific power range then the engineer needed to be sacked.
Why or what design issue would result in an engine, 0-360 A1A for instance, to be built with such limitations. Why would Thielert engineers allow their names to be put onto a design that fails so expensively?
Harmonics is not a dark art. Why complicate this issue? All we do is discourage any innovation within this industry. Lord knows, regulation has stifled light aircraft development into a multi decade old time warp.