Spec of bike: ZXR400 L9 18k miles on clock with alarm/immobiliser. 20 miles daily commute, 5 days a week.

Normal way to start it from cold: press button on fob for alarm to deactivate, put key in ignition, turn, dash lights come on and then press the start button and it fires up, normally without a problem.

The problem: upon pressing the start button, sometimes it will not start (starter motor turns engine over) and has no intention of starting, after further investigation this was found to be no spark at the spark plugs. When this happens, I simply turn the ignition key off and on a couple of times and then it fires up.

I don't want to be spending a fortune on replacing bits one by one, any ideas as to what is causing the problem? Its unlikely to be coils or anything, as all 4 plugs are affected Identically. I also do not think is is damp in the caps as they are in good condition and the bike runs perfectly once it fires up. I have a multimeter if there is anything I can check?

Any help is greatly appreciated!

I too have this problem. I have traced it back to the rectifier plug connections. I have wasted time cleaning them and remaking connections, this did help but the problem returns as crud and rain get in. My bike will start 99% of the time, the second it fails to spark I have to jam my hand up under the seat unit in front of the battery box and just prod the wiring loom in front of the connections on the rectifier, this works every time and I am good to go for another 99 starts.
I discovered this in desperation after my bike would not start after a fuel stop and a fore court strip down and rebuild. If this is the problem on yours the bike next time its turning but not firing - crank it over on the starter whilst giving your rectifier plug a wiggle it will either start up or you may experience backfire due to ignition (Spark) coming and going.
Hope it helps.
I don’t think I will ever fix mine but it’s not a problem when you know were to poke it.
ZXR400 L9 23000 miles on clock - had it from new and it has always had this quirk.