From a quick look, you don't have any commons connected to anything other than your opto isolators, so none of your valves should work (much less master valve).
On your picture it is really hard to differentiate between your common wire (connected to COM) and your master valve wire (connected to MV). Seems you've connected both of them to your opto isolator outputs which will not do you any good.
I would wait until Rachio support team looks over my advice, but here is what I recommend:
1) Find your common wire, probably one of those connected to your opto isolators
2) Connect it to any C terminal of Rachio on the left
3) Run a new wire from any available C terminal of Left controller to any available C terminal of Right controller.
4) Connect the white sides of isolator outputs to SC terminal of either Rachio (though right one may be best due to reduced load)
5) Connect the red sides of isolator outputs to your master valve line (which may already be connected)
In the future if you wish to get rid of isolators, you should be able to get a 24VAC 2 Amp supply and run both of your Rachios off of one supply (theoretically you can do it off of 1AMP supply you already have, but you need to make sure you are not running 2 zones at the same time). If you do this you could avoid the need for isolators and simply connect your master valve line to both of the M terminals (using something like the 3 way connectors you already have).