FWIW, I also believe it's a stale fuel thing. My Tenere was, for some reason, tolerant to being left standing, but my current bike and my WR250R are definitely not. Even so, my Tenere would reach the end of its patience after about 3 months (I worked away), and was very unhappy about it. It missed and stumbled, and tried to stall, and was generally "off" until the injector line cleared.

It depends on the fuel, obviously enough. Some go off earlier than others, and it seems to depend on the refuelling source, logically. High-turnover suppliers are best imo. Whereas my 250 often had fuel in it that was a couple of months old to begin with.