In watchOS 4 Beta 4 (and possibly later versions of watchOS 3), the WCSession isReachable comment is returning false and sendMessage fails if my watch fitness app running a workout session is not actively displayed on the watch face. This worked fine in earlier versions of watchOS 3.
The documentation of the isReachable property states:
WatchKit extension. The iOS device is within range, so communication can occur and the WatchKit extension is running in the foreground, or is running with a high priority in the background (for example, during a workout session or when a complication is loading its initial timeline data).
What I observe is that if the watch app is running a workout session in the background, isReachable is FALSE and sendMessage fails.
Can others confirm this issue or have any insights?