You should grab the manual, this way you'll be able to identify loose wires.. The coin door switch doesn't do much in fish tales besides blocking you from accessing the settings menu if the door is closed. In newer machine this interlock is used to cut off high voltage under the playfield. In your case, the switch needs to be opened so you can use the settings buttons.

Such intermittent issues might be caused by dirty/corroded connectors on the CPU board, dirty/corroded header pins on CPU, incorrectly connected connectors.. Or worse,battery acid corrosion (very common).

Can you provide a pic of the CPU board from battery holder down to the connectors, so we can verify the integrity of the board and verify for corrosion.

Have you tried unplugging the ribbon cable a few times at each connector? Or even better, to use a new one? It could also be a possibility. The pictures are small but the board does like clean.

Did you verify all voltages again just to rule that out ? You mention the reel and the playfield lamps both stopped working at the same time , but they are on different power lines with different fuses. TP1 in 12V unregulated, used for the reel, TP8 is 18v for the lampe columns but also feeds TP3 for the regulated 12v. All these voltages are present ?

Do all the boards have a good connection to ground ? Are they all screwed in tight ?