Waypoint adjustment on bomber escort missions

[RelentlessJPMoney]

This is driving me a little nuts. 
 

When playing P-51D career missions, most are bomber escorts. In my current career I am the squadron commander. What I’m noticing is that on some missions I am able to modify the waypoints for escort…at least the egress waypoint. I can’t change the waypoint where my squadron meets the bombers. But sometimes I can change the waypoint for the way back into friendly territory. 
 

Then other times, that ability seems locked. I can’t move any of the waypoints. This has occurred for me on the EXACT SAME MISSION when I have been killed and restarted the mission at a later time. 
 

What is the actual deal with changing waypoints in bomber escort missions?