Hi there!
So this has happened to me twice. I first got a mission to "Venus", and as I warped into it's SOI, the mission failed for no reason.
Then it just happened to me when headed to Niobe. I warped into the SOI of "Mars" and got a mission fail.
BUT it hasn't happened everytime. Previously I got a mission to get to the SOI of "Mars" itself, but that seemed to work.
Maybe it has something to do with how long it takes to get there? I had to plot some pretty funky courses being outside the ideal Hohman transfers. But the missions don't require a time limit to get there.
You were going past your deadline, this is fixed in the beta branch of the game, if things are stable it should be coming to the public branch this coming week