Titania, Uranus Tyl Regor Glitch

[(XBOX)Hells Hand]

The assassination mission constantly becomes locked when Tyl Regor on the 3rd phase teleports through the wall/door leading to the excavation point and then completely vanishes from the map.  I'm using Ivara's dash wire during the fight, no prowl, but even when I jump down he teleports through the wall/door.  Occasionally if I stand right up against the door I can get him to come out, but it's for about 2 seconds and he uses his knock back attack before I even know he's there, then it's off back through the wall again.  I have done this mission about 5-6 times and he has teleported through every time.  I'd like to get back to farming for Equinox parts but as you can imagine it's not fun wasting over half an hour on a mission to have the assassination target just up and leave the map through a locked door.

Edit: Tried again on Inaros, same result though, this time he split during 2nd phase.  After i attacked the first manic during 2nd phase Regor jumped up onto the second platform and teleported through the locked door making the mission impossible to complete.  Stood in the middle of the arena while I took a smoke break and was never so much as attacked in the 7-8 minutes I was gone.  Please let me know what's going on, it takes the draga quite some time to kill a maxed out Itzal and it's disappointing failing a mission over and over by no fault of my own.

Edit 2:  Ok did it today a few times on Frost making sure I killed the maniacs before I attacked Tyl Regor.  Is it possible the maniacs are teleporting into walls themselves where they are unreachable?  What determines when Tyl Regor is hidden away?  What are Tyl Regor's phase mechanics based on, just his health, a mixture of health and presence of any maniacs left on the board?  Is he supposed to be able to pass back and forth through the wall as he pleases during all phases or is this meant to be only during specific periods in the phase?  Am I supposed to play hide and seek with the maniacs?  Does anyone actually read these or am I just wasting my time asking logical questions?  

Edited February 10, 2019 by (XB1)Hells Hand