Try checking the coil spade end connectors before actually replacing the coils.

The vibes can make these go loose, which causes arcing and then you drop a cylinder.

You can spend ages running around, swapping plugs and components, when all you needed was a quick squeeze with some pliers.

The first time I had this problem I spent the time looking for bigger problems first. The next time I had the same problem on another bike, the first thing I checked for (and found) was a dodgy connection.

Might not be this but can save you a few quid.