Speaking from an EE point of view:
There is very little being drawn when the bike is off, but some power is likely being used for powering the ECU once in a while. They likely have a "wakeup" mode, where it wakes up every now and then, looks at the battery voltages, other various things, and then goes to sleep. This is in the milliamps, and likely takes only a few seconds and doesn't noticeably drain the battery. As far as I know, no other devices on the bike would be powered.
If you're seeing a SOC lower than you left it the night before, its likely because the battery voltage settle a little. Calculating the SOC is pretty much magic in my opinion. Its like trying to shoot a moving target while you're riding backwards and upside down on a horse that is running around a race track. Its not easy to hit the target and many times, estimations are used. As the voltage settles a little after a full charge, the SOC equation calculates a different result. There's nothing wrong with this, its just the nature of the beast, and I've seen it in ALL EV's that I've driven to some degree.
