It's always been that way for some things like bridge officer pathing or wander.
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Since it seems like whatever pathing changes made testing in preview quite unreliable, I'd like to see a possible solution:
A "Calculate Pathing" button, which basically publishes the mission on a dummy server that can be tested in foundry. Perhaps then a "Undo Pathing" button changes the preview mode back to the original. That way, we wouldn't have to deal with long waits while building, but we could then deal with long waits to test npcs, combat, wander, etc.
It's annoying, time-consuming, and sometimes detrimental to constantly have to publish in order to test.