A sort-of-known-problem with the Rex ignitions is corrosion/oxidation within the coil pack. Its failure will NOT record a fault code like a failed CPS will.

Tell your friend to dismantle the coil assembly (two torx screws sitting catty cornered to each other) and clean all mating surfaces and the two or three internal contacts. Assure that those internal spring clips are firmly contacting the pins that lock into them. There will likely be a bunch of dry crusty lube on the contacts. If necessary, tweak the springy contacts a bit to make them grasp more firmly onto the pins. It also wouldn't hurt to thoroughly clean the coil-to-chassis surfaces and apply a tiny swear of dielectric grease. I'm not sure if a good chassis ground is required or not, but it wouldn't hurt to address it anyway.

If the above doesn't fix it, then your friend may want to open up the distributor and look for oil leakage or any of the normal rotor and cap issues.

Were there any fault codes retrieved from the OBD system? Like CPS related?

Hey, did the timing belt beak?