It's my first time trying deployed science and I'm really not sure how it's supposed to work. The first one was really slow, so I deployed a second one (side note: are they supposed to duplicate infinitely? After I deployed the first one, my kerbin returned to the ship and then suddenly there was another one available?). It wasn't working, so I deployed a second solar panel (same deal with the duplication. I'm sure I only put one on the ship at launch). It still doesn't seem to be working.
Hmm. Did you place it with a scientist?
https://wiki.kerbalspaceprogram.com/wiki/Go-ob_ED_Monitor
There's also a proximity thing with the solar panels and control station. That left monitor should be good, but maybe the right one is too far away?
I've never had parts duplicate, but it wouldn't surprise me if you stumbled on some specific bug where that occurs.
Yeah I placed both experiments with a scientist and the control station & power with an engineer.
The guide linked in another comment says the range should be as much as 50 m, so I don't think range should be the issue? I could try moving it closer though.
I found this forum thread in which someone seems to have experienced exactly the same bug as me, in exactly the same circumstances.