1. The quickest/easiest thing would be for you to ask for them to show you in their client.
2. No, it does not affect it at all.
3. I have not seen similar complaints.
If the bid outcome shows they received their first choice, it could be a recollection issue. The only other thing that comes to mind is perhaps the schedule they are complaining about is not in the schedule bid effective window or someone made a change to their schedule after they bid. If you find that their first choice was not the one they received and bid outcomes shows they did receive their first choice, then I would suggest opening a support ticket so we could investigate further.