Does it only do it after a long ride? I take it it's OK on short journeys and when you just start it, run it, stop it, and start it again?

There are a number of faults that can cause the Engine Trouble light to flash when the starter is pressed - coil, lean-angle switch and a couple of ECU wiring related one that I can't remember off-hand. They all have higher number fault codes (higher than 12). Thing is the fault code displayed on the dash is only ever the lowest if there is more than one, so there might be something else afoot which you don't know about.

The long run/hot engine thing suggests maybe coil primary windings breaking down. Or perhaps a wiring fault which gives an increased high resistance when hot. I'm clutching at straws. Anyway, for now, if the crank position sensor is within spec and the wiring looks intact, check the coil and lean-angle cut-off switch. The starter relay (and start cut-off relay) can also give the flashing ET light, so check them too, as can faults with the associated components that feed the cut-off relay with data: side stand switch, neutral switch and clutch switch.

Unless you can get to/find a diagnostic tool (they aren't expensive and IMO well worth having), you won't be able to read all the fault codes if there are several (just the lowest). The bike's new to you, so is it under warranty? Trip to the dealer maybe?

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