Come Unstuck Meaning

(idiomatic, Britain) To get into trouble, to have an accident or mishap, to go off the rails.

Example: 1960, P. G. Wodehouse, Jeeves in the Offing, chapter XII:
  â€œWell, if you must know,” he said, “she's broken the engagement.” This didn't get us any farther. We had assumed as much. You don't go calling people rats if love still lingers. “But it's only an hour or so,” I said, “since I left her outside a hostelry called the ‘Fox and Goose’, and she had just been giving you a rave notice. What came unstuck? What did you do to the girl?”