How do the LEDs function in the different modes?

Preset: LEDs A-C represent presets 1-3 in the connected pedal(s).  The LED states indicate which preset is loaded. If no LEDs are lit on Multiswitch Plus, then the connected pedal(s) are either bypassed or the onboard preset (preset 0) is loaded.

Tap, Fav, Boost & Speed: Depending on how MultiSwitch Plus is configured, the LED indicates that the FAV setting is activated, Boost is engaged, or Fast speed is selected.

Timeline, BigSky & Mobius: The LEDs do not function in this mode because communication with TimeLine, BigSky and Mobius via the EXP jack is not bi-directional.

Custom: The Custom setting functionality and LED behavior varies depending on the settings selected on the connected pedal.

Combo: In Combo mode, LEDs A-B indicate the selected preset for the pedal(s) connected to jacks 1-2. LED C indicates that the FAV setting is activated, Boost is engaged, or Fast speed is selected for the pedal connected to jack 3.