My understanding is that 4 Senators (Collins, Paul, Lee, and Moran) announced opposition to the bill floated at the end of last week, whereupon McConnell- with support of the White House- then said his next step would be a repeal-only bill with a replacement (maybe) in 2 years.

https://www.washingtonpost.com/powerpost/trump-suggests-republicans-will-let-aca-market-collapse-then-rewrite-health-law/2017/07/18/5e79a3ec-6bac-11e7-b9e2-2056e768a7e5_story.html?hpid=hp_hp-banner-main_healthcare-844am%3Ahomepage%2Fstory&utm_term=.e96e4af0da78

Then, "three centrist Republican senators — Susan Collins (Maine), Shelley Moore Capito (W.Va.) and Lisa Murkowski (Alaska) — all said they would oppose any vote to proceed with an immediate repeal of the law." That is what I think killed the last iteration.