I'm having the same issue. It crashes the first time it is run. Running the app again doesn't cause a crash.
This is what I noticed:
1. Running the Watch app manually with Xcode attached causes the watch app to open, close, open again and work. No crashes registered.
2. Installing the app from the Watch application, then once the app is installed (finishes loading on the Watch) unlocking the device with the Watch iPhone app in foreground, then opening the watch app for the first time doesn't cause the app to close.
3. Installing the app from the Watch application, then keeping the iPhone locked with the Watch iPhone app open, then opening the watch app for the first time (once it finishes installing) causes the watch app to close.
The Apple Watch device logs for a crash scenario (#3) shows:
Sep 9 15:59:37 Cezars-AppleWatch iap2d[222] <Warning>: process com.***.yyy.clockapp is now running the foreground
Sep 9 15:59:37 Cezars-AppleWatch gizmoappd[88] <Notice>: (Error) WatchKit: <SPGizmoPlugInManager.m __59-[SPGizmoPlugInManager sendToPlugin:clientIdentifier:call:]_block_invoke:1115> The first pended call for com.***.yyy.clockapp was more than 30 seconds ago, so will attempt to force a load of the plugin
Sep 9 15:59:37 Cezars-AppleWatch gizmoappd[88] <Notice>: (Error) WatchKit: <SPGizmoPlugInManager.m __59-[SPGizmoPlugInManager sendToPlugin:clientIdentifier:call:]_block_invoke:1122> plugin com.***.yyy.clockapp appears to be stuck loading. trying to force it to quit
Sep 9 15:59:38 Cezars-AppleWatch gizmoappd[88] <Notice>: (Error) WatchKit: <SPGizmoPlugInManager.m __59-[SPGizmoPlugInManager sendToPlugin:clientIdentifier:call:]_block_invoke:1130> after waiting for 1.0 secs, endUsing: callback for com.***.yyy.clockapp never fired. Giving up and hoping the next load attempt works
And that is followed up by (after a few duplicates of the log above):
Sep 9 15:59:39 Cezars-AppleWatch securityd[68] <Error>: CFReadStream domain: 12 error: 8
Sep 9 15:59:40 Cezars-AppleWatch kernel[0] <Notice>: xpcproxy[783] Container: /private/var/mobile/Containers/Data/PluginKitPlugin/BB622000-8DEE-4132-9FD5-C5F9C9DF6563 (sandbox)
Sep 9 15:59:40 Cezars-AppleWatch gizmoappd[88] <Notice>: (Error) WatchKit: <SPGizmoPlugInManager.m __59-[SPGizmoPlugInManager sendToPlugin:clientIdentifier:call:]_block_invoke:1130> after waiting for 1.0 secs, endUsing: callback for com.***.yyy.clockapp never fired. Giving up and hoping the next load attempt works
Sep 9 15:59:40 Cezars-AppleWatch join.me WatchKit Extension[783] <Notice>: (Error) WatchKit: ComF: -[SPRemoteInterface _interfaceControllerWithID:] interfaceController for interfaceControllerID:30E0002 not found (clientIdentifier=(null))
Sep 9 15:59:40 Cezars-AppleWatch gizmoappd[88] <Notice>: (Note ) WatchKit: -[SPGizmoAppServer notifyClientsExtensionTerminated:] Companion app extension died - killing gizmo app com.***.yyy.clockapp
Sep 9 15:59:40 Cezars-AppleWatch gizmoappd[88] <Notice>: (Error) WatchKit: <SPGizmoPlugInManager.m __59-[SPGizmoPlugInManager sendToPlugin:clientIdentifier:call:]_block_invoke_2:1126> got plugInExited: callback for com.***.yyy.clockapp
Sep 9 15:59:40 Cezars-AppleWatch assertiond[51] <Warning>: Unable to obtain a task name port right for pid 783: (os/kern) failure (5)
Sep 9 15:59:40 Cezars-AppleWatch gizmoappd[88] <Warning>: plugin com.***.yyy.clockapp.clockextension invalidated
Sep 9 15:59:40 Cezars-AppleWatch Carousel[30] <Warning>: BSXPCMessage received error for message: Connection interrupted
Sep 9 15:59:40 Cezars-AppleWatch Carousel[30] <Warning>: BSXPCMessage received error for message: Connection interrupted
Sep 9 15:59:40 Cezars-AppleWatch Carousel[30] <Warning>: BSXPCMessage received error for message: Connection interrupted
Sep 9 15:59:40 Cezars-AppleWatch Carousel[30] <Warning>: BSXPCMessage received error for message: Connection interrupted
Sep 9 15:59:40 Cezars-AppleWatch iap2d[222] <Warning>: process com.***.yyy.clockapp.clockextension is now terminated
Sep 9 15:59:41 Cezars-AppleWatch join.me WatchKit App[782] <Warning>: -[SPApplicationDelegate extensionDidTerminate:] WatchKit App killed by WatchKit daemon
If you follow the steps described on item #2, then you don't get the crash. That happens because the Apple Watch is able to acknowledge the install status, which doesn't happen on situation #3:
Sep 9 16:16:19 Cezars-AppleWatch gizmoappd[88] <Notice>: (Note ) WatchKit: applicationWithIdentifierWasInstalled, installed (com.***.yyy.clockapp)
Unfortunately my Xcode is stalling when I try to see the available crash logs, but as far as I can currently tell, no crash logs were registered.