AiTravel maximum range depends on "actors processing range" setting
AiTravel package is supposed to have the maximum range the 7168 game units. It is the distance between actor and target, not between actor and player, but we erroneusly use the "actors processing range" setting value here.
As a result, with the low processing range (the 4000, for example) AI considers the target of long-ranged AiTravel packages (with the distance of 5000, for example) unreachable and actor does not move.
The simpliest way to fix this issue is to use the 7168 cap indifferently from processing range again. In this case actor will move to target, but will stop near behind border of the processing area.
Note: Morrowind processes AI packages on distance of 7168 indifferently from "AI processing range", but if we want to replicate it, we will have to update physics as well. Maybe it is worth to do, though.