Does it come back, or did it never go away even for a second when you changed the spark plug, coil, and injector?
Could be iffy wiring to the coil if it is/was intermittent
Could be a a busted rubber or body damage somewhere or a coolant expansion tank leak allowing liquids to get into the spark plug well if it first went away but returned later
PS #8 should be rearmost driver's side, is that the one you swapped? I know it sounds like a funny question, but these things happen. And apparently some cars number em differently