In chaos tiers, the lines were removed entirely. 

Ah yes, after looking into the patch notes they were indeed removed. I just came back to the game recently. However few path lines still show up in the chaos tiers in some maps which is a bug i guess :)

Sometimes I don't see the pathlines in normal missions as well.

My brother and I play together often and see this issue on very many maps occasionally we will see the lines show up then disappear again but most of time they are gone every since the patch it seems.

If it was intentionally removed in chaos tiers, then I saw it yesterday in Chaos 2 during either the Ramparts or the Attack on the Ramparts mission. It's inconsistent which is probably why we're wondering why we see it sometimes and not others. I don't really get why they'd hide it at all even at chaos tiers. It's not some huge advantage.

from patch notes,23 aug

 Wisps are back on all game modes!

still not working , in chaos

Cyborg, what about now, is it working ?

last few days it is working

i will keep a eye on it

did not play many maps