One thing to consider is that this seems to be happening once the bike has warmed up to operating temperature. No owner said they had the problem during cold, initial starting. This tells me that the heat from the engine compartment, possibly combined with road vibration, is precipitating some electrical connectivity or current passage failure once up to temp. The starter could be allowing the bikes electrical system to be shorted to ground intermittently and depending on where that short is occurring, system voltage dives and everything resets a fraction of a second later. I am not saying that is what is happening, but it could be one of the possibilities. It could be very difficult to find out just where this fault is occurring. But if your battery starts your bike ok when cold...why do you suspect a battery problem later in the day?? That makes no trouble-shooting sense at all. If the starter seems to be more labored in its turning of the engine when this occurs, it is obvious that the starter is not getting the correct voltage at the needed current to give it the power it needs to spin properly. This does not mean that the battery is necessarily bad, but it does mean that there is something happening somewhere within the electrical path that is preventing the starter from acting normally. I would definitely suspect that a wiring harness issue, bolted connection, or possibly a switch (and yes including the ignition switch) is to blame here. As you have read, this still happens with a new battery....so I am sure this is not just a battery issue.
