Sally 3 brilos there are multiple right answers, but one is always wrong.
Afraid I know of no solution but this is the second time somebody’s mentioned a similar problem in the past few days. This is a thread about duplicated correct answers on a sign language course, with neither appearing correct when selected.
Time for a bug report, I think. You know… once is happenstance, twice coincidence, etc.
Hard to say whether the courses’ve not been constructed correctly in some way, or if this is a global issue with multiple selection questions. Though, you could turn off multiple selection questions to avoid it, I guess.