The PCM can cut cylinders for reasons, there is a DMR logging parameter that shows how many cylinders are active. AFAIK it will cut half of the cylinders via injector cut for various FMEM reasons ie: overboost, etc. There is that side of things.
Onto losing power at the injector, they are 12V live all the time and the PCM pulls them to ground. First check for pin connection, it is common to have issues there. Either the pin will back out of the plug or it will open up inside the plug and cause issues. Pigtail connectors for aftermarket injectors are notorious for this. If there is an intermittent fault with the injector 12V, bypassing it with a direct battery feed will show results. Literally run a wire from the battery positive to the injectors in question and that will rule that out.
Other things I've seen, the coil cover fasteners can pick up the coil or VCT loom under the coil cover and can earth it out through the rocker cover.
I can see you've checked some of this, it can pay to double check things, especially if you've been rushed.
I haven't opened up a PCM and can't say what will fail and at what age, however I have seen a few dry solder issues with white goods that are easily fixed. This would be the last place I checked, unless of course you have access to another PCM that will run the car.
Hopefully there's something there for you.