Chester's evening offer has been a bone of contention for a while.
Connecting to or from a 21 is painful. 
I've been known to stay on a 21 all the way through to Durham and get a 20 from there, rather than endure a wait for the 36/71. Those who have read my thoughts on the vehicles allocated to the 20, will be aware of the torment that caused.

Obviously on a Sunday it is impossible to do get a 71, so it means going via another route (and having a valid ticket covering you for the alternative) or not bothering with the bus at all. 

They seem to have improved the 78/71 evening departures from Chester towards Great Lumley. However, if you're in Great Lumley and looking to get to Chester (or beyond) on an evening, the timetables aren't the best.