How often on B1 flights do the engineers find any faults?
Technically speaking there are no engineers on B-1 flights. There is a pilot and copilot, most of which have a degree in engineering but aren’t using it, a systems operator (or whatever they may be calling it these days) who is sorta like the old flight engineer (who assists the pilots doing checks in the cockpit) and one or two flight analysts who handle the back end and support the flight crew relative to technical information — none of these people are engineers generally.
Getting back to your question, the B-1 crews find faults almost on every flight — some of more concern than others. If there’s a B-2 or C-2 flight it means whatever faults were found require a reflight to be cleared.