Imminent Mission Failure... even after killing all required enemies?!

[Btabc]

So I was hunting Lua for caches (found 2 of them) and was about to obtain the third for the systems for Octavia when I get a mission failed due to not killing all the required enemies?!  I killed the 160/160 and any others that were still around, ran the map several dozen times and did not find anymore enemies or caches, however on my way back I was able to find the last one!  Now before getting back to extraction I got the warning  and had 40 seconds to get back to the extraction point, but right before I got there I failed the mission... is this supposed to happen?!  Has there been a time limit on how long we can stay on a map?  

 

I am, unfortunately, not able to provide a screenie because I was too focused on find that last cache.  It's not the end of the world for me because I can go again, but I was just wondering if this has happened before?

[Voluundr]

The time limit appears when you don't kill any enemies for a set period of time.
Leave one or two alive nearby to delay the timer if you want to go cache hunting