Invader lair is removed from kingdom too soon
Invader lairs used to last until after the invader was gone from the kingdom. Now, it seems I cannot even farm an entire lair before it is removed. I can even [try to] send troops while others are still returning from a yield, but "the resource is no longer at the coordinates" or something similar pops up. A fresh level 6 invader kill may leave a lair with 2.2m iron, but after making only 2 trips yielding 150k each, the third attempt to yield/farm the lair results in the "coordinates" message. As an additional observation, the invader may still be active for 6 or more hours. Today it happened on Barbarians, but this has happened to me on Serpent lairs, Northern Vulture, Cave Lion, and Canis too.
This is not a case of clearing cache so that the lair no longer appears, but a case where the lair SHOULD still be available for yielding.