CUIThemeStore: No theme registered with id=0 on Watch Extension on device

Question

When I try to execute my app on my Watch I get

AppExtension [framework]: CUIThemeStore: No theme registered with id=0

while the code rests on

lybsystem_platform_dlyb'_platform_memmove at line 23.

No error comes out instead when I execute the app on the simulator. The error seems to pop up between applicationDidFinishLaunching() and ApplicationDidBecomeActive() . If I try to have the execution progress, it ends for the better with:

Terminated due to memory issue.

I use Xcode10.1 with an iPhone XS with iOS 12.1 and watchOS 5.1.1.

How may I know better and fix the issue?