I don't know how you managed to pry open that plug boot to the point the circlip flew off, but the thought occurs to me that the silicon liner inside that cap may have been damaged in the process. If that were the case, spark can short circuit from the wire to the case, easier than it can bridge the spark plug gap. This happens frequently after a rough landing, where the spark plug cap has engaged the dirt, so replacement parts are available reasonably.

If you can hear the spark snapping, but you can't see it bridging the plug gap, that silicone liner is your issue for sure. Problem is you can't always hear it. When you can is a dead give away though....

Also, the plugs supplied with the DLE engines have a terrible reputation. Most recommend they be replaced immediately with an NGK CM-6.

Last, one end of the diode is stuck in the center of the spark plug wire as it enters the cap, and the other end engages the small spring seen deep inside that cap. Anything is possible, but the chance of that being an issue are pretty remote.

Have patience, you'll get through this.....