Possible bug? 2 heroes 'disappeared' on Recon.

I have a problem... I sent 2 heroes on a 8h recon mission last night. This morning of course I have a notification that the recon mission is complete. I boot up the game and even have the ! icon on my planets signifying the recon mission is back. But when I open the planets menu, I don't get the popup offering to replace the discovered planet. I can navigate to the Recon submenu and even start a new recon mission - but my 2 heroes didn't come back!

In the Hero menu, those 2 heroes still have the recon logo in the top left corner as if they were still out on recon... So what do I do? I don't really care about the mission itself but I do care about 2 S-class heroes just vanishing without explanation. And now they are occupying 2 hero slots while I can't use them for anything; I can't even dismiss/retire them!

Is this normal? Did I miss something? How can I get my heroes back??