Vegas' goalies can't stay healthy/consistent. Hill came back from an extended injury and played so well people, even outside Vegas, wondered if he could contend for a Vezina (but most felt he wouldn't have enough games played). Then his game completely tanked to the point that I'd put around 4-5 losses being directly impacted by Hill not making 1-3 very stoppable saves, but Vegas kept starting him hoping he'd turn it around and he got injured again. Logan Thompson stepped in and played a stretch of really good games, but the last two were pretty rough and he left a recent practice with what Cassidy called a non-serious injury. Either way, unless one of these two guys seriously locks in, I see it as a big issue going into the playoffs.
Vegas as a team has had a big issue with third period effort. I think, in general, the team has had a weird game approach all year where they have this air about them like if they play a highly technical and responsible style of hockey, they'll simply out talent/out sophisticate their opponents, but that hasn't always carried with it a gameday approach of outbattling their opponents. The Vancouver and Arizona games are bigger examples of the Knights just taking their foot off the gas with a lead in the third period. Vancouver didn't make them pay for it but the Coyotes sure as shit did with that 6 goal period.
As a whole, I feel like age is starting to catch up with some of their veterans like Martinez and Pietrangelo. I don't expect a follow up run this year to be as defensively tight as it was last year.
Then there's the issue that Vegas hasn't even locked in a spot just yet. They could still lose out and concede their spot.