Closing as not a bug. From the manual with emphasis added:
[quote:32mtn3ft]Regenerate obstacle map
Determine whether each cell in the obstacles grid is an obstacle again. This is a very CPU intensive action and should not be used regularly. If only part of the obstacle map has changed, prefer to use one of the Regenerate region actions. Any changes made by using Add obstacle, Clear obstacles, Add path cost and Clear cost will take effect the next tick after this action. Note this means if you attempt to find a path immediately after this action, the obstacle map won't have been updated yet; add a 'Wait' action with a short delay to make sure the updated map is used in that case.
Your project regenerates the obstacle map and finds a path in the same event without waiting for the update.
The Pathfinding behavior has worked like this as long as I can remember and we haven't changed the behavior at all for some time now, I doubt it used to work.