Most likely the wiring loom to the coil packs has degraded with heat where it rests on the cylinder head .
This loom is a short length that plugs into the main loom and just goes to the coil packs . It is designed to be replaceable and just unplugs . Awesome GTI site used to sell them, otherwise your seat dealer will have them . When it goes it generally shorts on the rocker cover or internally if the plastic covering has degraded . This blows a fuse so you will need to check all your fuses after replacing . Other than that a flat battery , poor earth on earth strap , or failed coil packs are likely suspects.