I have adopted the new background task API in watchOS 3 and my complications start updating as expected. I have a single background task that gets scheduled every 30 minutes, so I should only be using 48 of the 50 updates per day given to the complication (mentioned in the Keeping your Watch Apps Up To Date WWDC video). However, it seems like the complication often stops updating. This is particulary noticable after the user takes off the watch and it is locked for several hours (such as when they go to bed overnight). The next morning the complications don't start updating until I manually launch the watch app. This is particulary odd because I only schedule a complication refresh when a background task is fired, so launching my app that was still in memory (verified because of how fast it is launching) does not cause the app to refresh. It seems like the background tasks are suspended for a time when certain conditions are met and are not being re-initialized.
Has anyone else seen this issue? I have noticed that having the app in the dock seems to reduce the likelyhood of this happening, but does still happen on ocassion.