Multimove and manually snapping to grid

It is possible to change "start" end "end" properties of the additional selected events in onEventMoving. You can modify the args.multimove[x].start and args.multimove[x].end properties as needed. Just note that the first item in the args.multimove array is the master event - the custom "start" and "end" property change will be ignored (use args.start and args.end instead).

The following example resets the start and end of all additional events in the selection to the position of the master event:

onEventMoving: args => {
    const e = args.e;
    args.multimove.forEach(x => {
        if (x.event.id() === e.id()) {  // ignoring the first item that
            return;
        }
        x.start = args.start;
        x.end = args.end;
    });
}

You may need to review your logic to see if the start/end properties are being set to the correct values in your onEventMoving handler.