Now here is a weirdness. My subdued cave lion can only move out of a fort to one plot. It can't move to any of the other land plots! All plots are in my territory and have no enemies on them. Other units can move to all valid land plots.
The fort is between Giza and Akhetaten.
Edit same thing happens with other subdued animals coming from the East. Since they can move into the North East plot things coming from the west have no problems.
It looks like a ZoC problem. However having units to the west does not help.
Nothing to do with ZOCs and actually quite a subtle bug, revealed by the super forts changes to visibility!!
The subdued animal cannot move in such a way as to reveal new terrain. The fort adds 2 to the visibility range of units in it.
The bug is that the check for whether you would reveal by making move uses the visibility range at the plot you are moving FROM to assess what is revealed from where you move TO. This is clearly wrong, and is why your subdued lion cannot move west.
In PRINCIPAL it would be possible that the corrected version of this test will prevent a unit moving INTO a fort, but in practice that could only happen if the fort was (and had been historically) unoccupied by any other of your units with at least as much base visibility rang as the subdued animal (highly unlikely)