This thread has all the details of several of us trying to troubleshoot it. The specific post I linked to has my excessively-detailed steps to consistently reproduce what seemed to be an intermittent issue (but you bought an Inovelli switch, so maybe you like excessive detail 
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I don’t understand all the electrical details of why it doesn’t work, but it’s something along the lines of “the capacitor that’s included in the switch and necessary for AC Ceiling Fan speed control is always part of the circuit, no matter how it’s configured, and under certain conditions it does some electrical thingy that makes certain DC exhaust fans not work”. It’s a hardware issue that cannot be fixed in software.