Attached a screenshot. I can not assure that this is reproducible, but I will try later. Basically I joined this second mission, won it (result was 100% for my team :D, pwnage (on both normal and hard difficulties)). Then I got back to deployment screen -> mission selection -> main menu -> option -> turned off blur -> main menu -> missions = no button “Deploy the fleet!” 
cripes that’s weird. I will investigate to see how you have managed that 
I cannot actually work out any way in which this is theoretically possible. I’d love to know how to reproduce it so I can fix it…
other note: even if i selected other missions, there were no button. Restarting game helped. Can it be anomaly if i alt+tabed the game?
I did not manage to reproduce this bug yet.
PS: I HAVE JUST REPRODUCED IT, trying two more times and will give instructions in next post.
Since my english is not that good… Here is video.
To recreate the buggy behaviour just run the game, goto battle, click on some mission labels, return to main menu and then come back to battle (mission choice menu). No button for me.
OS: W7, 7100
GC: nvidia gtx 280
I found a way to fairly reliably reproduce it, and expect that I have now fixed it (for 1.16)
Cheers