It's so hit and miss.
Downloaded a couple of episodes of Justified the other day, went to play the first and said it had expired, the other just disappeared.
Grabbed Arrow and a Blacklist and watched with no issue yesterday, just grabbed the next Blacklist and midway through downloading the Hudl lost wifi and wouldn't reconnect. Rebooted and now clicking the Sky Go app opens and shuts it within a second, rebooted again and no change.