(Woo, I can ask publically, since the PnP files were released!)
Some Fear cards can earn Fear themselves. For instance, the Dahan Raid fear effect at Terror Level 3 could cause quite a lot of damage to the invaders and earn a lot of fear. Suppose this earns another Fear card. Does it get resolved that same Fear phase or not?
When this came up in playtesting, the answer was no. You basically pick up the stack of cards and resolve them. Any cards earned form a new stack that get resolved the next turn.
Thanks! That makes sense, and is easier to implement.
Update: the final rules will almost certainly change this answer to "add the new Fear Card to the bottom of the stack of cards you're resolving this Invader Phase".
(While writing the FAQ for this question, I realized that "delay it by a turn" was... not inconsistent, but slightly incoherent with Terror Level increases applying immediately. Also, there's an argument to be made for rarely-relevant edge cases with minimal play impact to err on the side of permissiveness.)
It really doesn't come up very often, though, so it's not much of a change.
Oh cool. When I first started playing the game I assumed that this was how it worked, so I'm glad that this is now official.