Failing 100% success missions?

I FINALLY got my main to 120, and went back to play an older alt that I have not messed with in a while…
She was a Hunter, who is still in Draenor, at her Garrison. As soon as I loaded her, she was in her town hall, so I clicked the mission table to see that she had 2 completed missions. The first mission had a 100% chance of success, so I did not sweat it, but it still came back as failed?? The other had a 32 % chance, so of course that failed, RNG is evil sometimes, but how can a 100% fail exactly?? Doesn’t 100% mean guaranteed to win, or am I mistaken??
Please clear this up for me, and Thanks in advance!!