Every message lands at the worst possible moment
The enquiries do not arrive during a quiet Tuesday afternoon. They arrive at 7:30 on a Friday, when the pass is backed up and every person in the building is needed where they are. So they sit. By the time anyone looks, it's 11pm, and the table for six booked somewhere that replied.
The questions are almost always the same handful: is there a table on Saturday, do you have anything gluten free or vegan, can you seat a group of twelve, is there parking, are you open the public holiday. Every one of them is answerable without a manager — they just need answering *now*.
This is a timing problem, not a service problem. Your team is doing exactly what they should be. The gap is that nobody is free at the precise moment somebody is deciding where to eat.