Running iOS 12 b3 on iPad, created a shortcut which works just fine. Added a Siri trigger and this selects the right shortcut, displays 'running your shortcut' (correct icon appears) but then dispalys 'sorry, there was a problem running the app'.
I tried setting a Siri shortcut to view recent phots on iPhone and this worked (on iPhone and iPad)
Anyone managed a personal Siri shortcut that launches a Shortcut?
Sometimes mine work and sometimes they don’t. Ive seen the behavior you mention. I’ve also see it actually launch the app and then do nothing or freeze. It’s still pretty buggy.
I suggest you file radars with your specifics. I’ve done the same.