It seems to me, from the conflicting experiences, that the issue is they can't match staffing levels with demand, so when demand is low they have plenty of staff on duty and everything runs fine, but when demand is high they have the same numbers on duty, and it's a disaster.
So either management is too incompetent to forecast demand (which should be easy) and ensure that sufficient staff are on duty, or the staff are too inflexible to respond to variations in demand, which is also ultimately a result of incompetent management.