My Monday morning quarterback opinion, is that it is station/IG entrance construction issues that caused the "delay".
While they could have pushed construction, that can cost you money. Without the Riviera open, there really is no operation need to have any of it run or rush into it. So take their time on the infrastructure stuff and open when ready. I'm sure 2/3rds of it could open now, but might as well open the full thing so you don't have to half bake your grand opening.
Cable stretch is a non issue, it's a normal thing to deal with. Add in a little Dorian drama and here we are.
I'm sure they want to make look as polished and complete as possible, despite their recent trend to open quickly and not 100%.