As title says, once a unique has retreated, LITW will no longer hit it until it gets into combat again. Reveal creatures does not have this bug, as shown above.
On indy with a pendulum that has about 150 tile range so its not like it sprinted that far in 8 seconds, could physically see it when getting no hits with the pend
This was happening before the hotfix that happened before, it worked as normal until it aggro'd again then proceeded to not work any longer
Edit: this happens for all champions, quite often i'd be walking towards a champ that's directly in front of me, then suddenly pend wants me to turn around because a different champ is quite some distance behind me. Champions move a lot so its pretty hit or miss if a pend will hit them constantly