Plugs

I had a similar issue with a smart switch rated for 15 amps that kept tripping at around 12 amps with a motor load. What I learned is that the rated amperage on these devices often assumes purely resistive loads like heaters or lights. Motors and heat pumps have a high inrush current when they start, and the switch might be detecting that momentary spike as a fault. Also, the autotransformer adds another layer of complexity because it changes the current draw characteristics. The switch might have a built-in protection circuit that is too sensitive for inductive loads. I solved my problem by using a contactor between the smart switch and the load, so the switch only handles the low current of the contactor coil. That way the heavy current passes through a device designed for motors. You could also try a different brand of switch known for handling inductive loads better. I had to document my setup and send the details to the manufacturer, and I ended up using an app to send a fax from your phone because they wanted a signed document. The V2 seems like an improvement, but 1100 watts might be right at the limit of what the internal relay can handle consistently. It's worth checking the datasheet for the specific relay model they used.