Given how wasted spark works...the chances of 1 cylinder not having an adequate spark is pretty slim, and if it is, it will either be the coil pack itself or the HT lead...very unlikely the HT lead unless it is visibly bolloxed. But easy to swap leads with another cylinder

Swap the injector from another cylinder to see if the problem moves.

Faulty injectors are rare, but it is possible.

I could also question mechanical integrity, even if you do say compression test etc is ok But try the above.