[arbiter]

But the path being null is the problem.
It just found the same path numerous times before, then suddenly it doesn't exist.

Is it the exact path? A path is defined by a start point and an end point. Are those the same? I highly doubt it, because that's not how algorithms work. If not, then it's likely not in the same Region. As discussed earlier if the destination is not in the same Region it's impossible for RegionPath to make the path.

Solution: Use different path solutions like WebPath or BresenhamPath when RegionPath is not possible.