Many thanks for your post. I was struggling with the RTC not working, and this made me aware of the issue and the trivial fix.
I am an electronic n00b, and this was my first project putting together a PCB&circuit, so I feel rather satisfied now that everything works!
Here are a couple more hints:
On point 2), Resistors LT and RL, used in the current sensor circuit, must NOT be mounted on the PCB. They lift the ADC input voltage above 1V and permanently saturate it. Found it the hard way and ended up simulating the circuit before I understood the problem. Leave them out and the circuit becomes a rectifier of the input voltage as intended.
4) The LM1117 linear regulator on the Master PCB is a fixed 3.3v model. I mistakenly bought an Adjustable model and it obviously did not work (BOM does not specify and not knowing there were different kinds of LM1117..).
The AC driver board worked fine by just following the schematic. There seems to be no issues there.