I have noticed what I think is a ceramic capacitor missing as show in my photos. And from my very limited knowledge it looks like its leaving a
section of the board disconnected from the circuit. Could this be part of the problem?
No, most unlikely.
That is a "Y" capacitor which forms part of the noise filtering circuit on the mains input.
Fault diagnosis from pictures on the internet is always difficult, going on impossible.
But the intermittent nature of the fault suggests to me that you may have a bad solder joint somewhere.
The usual suspects for this are large components, like the big capacitors, the transformers/coils, and things that get hot like those transistors mounted on heat sinks.
Examine the joints carefully, try and wiggle the component, does the wire move in the solder fillet?
Or you could just try re-flowing the solder joints.
Just touch them with a soldering iron to melt the solder for a second and than take the iron away.
It is also worth looking at the solder joints on the off board connector pins, they can sometimes become broken.
JimB