WatchOS not updating complication

I have made a trivial app that provides a complication. The complication updates every minute. The problem is that the complication keeps stopping updating.
When my app starts, WatchOS is calling

getTimelineEntries

with

after=now

and

limit=100

, then calling it again immediately with after set to 1 minute before the last entry I created, then again a second time. The complication appears and starts working fine, however a few hours later it is generally not updating any more.

In

getTimelineEntries

I am calling

WKExtension.shared().scheduleBackgroundRefresh()

with

withPreferredDate

set to 10 minutes before the last timeline entry I created. In the background handler I am calling

CLKComplicationServer.sharedInstance.extendTimeline()

for every active complication.
It's hard to tell exactly what's going on as I can't work out how to view the debug

os_log()

messages that I've added, when the app is running on my actual watch as opposed to a simulator.

So, (a) how do I get WatchOS to reliably call me to update the complications when it runs out of pre-calculated ones, and (b) how do I view

os_log()

entries (I can connect to the watch in the Console app but it doesn't show any log entries at all).