Why does my beloved VRS keep developing a misfire?

Hello, I have owned my VRS for 6 years now, the best car I've ever owned. Used to go through cars as often as I changed phones. Wondering if anyone can shed some light on a recent problem that I'm having. A few months ago a misfire happened, I had an ignition coil replaced in cylinder 1 and was told that when 1 went the others would more than likely give at some point soon too. Sure enough it happened again and to save some money on diagnostics etc I bought 3 more and replaced the others. In a short amount of time the coil in cylinder 4 has failed twice and now the coil in cylinder 2 has failed. Once a new coil is in the car runs perfectly again. I have replaced the spark plugs between fails to try to rule that problem out. 

Is there a more sinister problem at work here beyond the ignition coil wiring or could it be due to the fact the 3 I bought were relatively cheap in relation to further replacements I have since bought?

I have tried to see if there are past posts relating to this issue but I can't see anything this specific.

Hope someone can help.