After 12 hours of stats observation I've the impression that a loop of map creation (from both direct mapconfig and from template instanciation) and a subsequent fetch of a single PNG is not enough to stop MapConfig items in redis from expiring hourly.
This is with NO mapConfigTTL configuration, so theoretically with the default of 1-hour expire.
This should be inspected, and ideally a test should be written for this.
Found the culprit: CartoDB/Windshaft#160
This is really a duplicate of #159