question

When dealing with staff from the people module, always acquire them before giving them tasks. There is a hidden Process Flow that makes them return to the reset position when they become idle. This flow waits for them to get acquired to abort the task. If you give out other tasks without acquiring them the return task stays in their task sequence queue and eventually leads to an the error.

All patients wait in the same Waiting Line object. When either desk becomes available they will travel there. In your screenshot you can see that both desks are currently being used.

Validation will need to be done by you, since nobody else on this forum knows how the model is supposed to work. Follow a couple patients through the flow to see if everything works as expected. Do the same for other logic such as the replenishment. And check if the overall throughput seems reasonable given the number of staff, locations and process times.