I’ve been able to replicate a situation in which launched interdictors do not land after running their defensive pattern. In all cases, I was launching two lvl 6 craft and using Aegis Pattern. If neither fighter is hit for damage, then both will land normally. If either takes any damage at all, both craft will remain in space without landing for the remainder of the combat. In one fight, the hit craft had a debuff applied to it. In other fights, it did not, so it seems that it is the damage itself causing the craft not to land.
The main ship did not get hit in any of these fights, and in particular, there was no damage to the launch bay or hangers.