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I didn't get to read your message until this evening, so it was too late to check for solar panel HF interference. I'll have a look in the morning, but I can't recall ever seeing spikes like those in your screenshot (thank goodness!). My first thought was VDSL, maybe radiating from some faulty equipment. Is it there during daylight only, or all the time?
I did find that 144kHz signal from the Envoy to the microinverters, though. It looks like another pulsed signal, but much weaker than the 16kHz cluster, and faded out around 17:13, so there's no doubt as to where it was coming from or what it's linked to. I think this is now "case closed"!