Eagle-eyed fans noticed a photo that Michael Rubin's daughter, Kylie, posted on her Insta Story from Sunday ... which shows her sitting next to socialite Will Makris (the dude sleeping in Kim Kardashian's suite) -- and while she was cracking jokes ... others were zooming in on her pic.

The reason for the focus ... Devin Booker was chillin' in the back, seemingly trying to be low-key and enjoy his food -- but certainly sticking out like a sore thumb regardless.

There didn't seem to be anyone else around him in this photo, but the fact he was even there at all -- in the KarJenner suite, no less -- caught the attention of many ... and for good reason. Obviously, he's one of Kendall's many famous exes, and a more recent one at that.

No explicit evidence (yet) that he was hobnobbing with Kendall specifically, but ya gotta figure he was there because of her. Even more fascinating ... Bunny was also in the building.

Photos have been circulating of the Puerto Rican rapper/singer hanging out with Lizzo's crew -- all of whom were rolling with Apple honcho Tim Cook, it seems -- and they were all in a completely separate private suite ... in a completely different part of the stadium too.

On its face, it would appear Kendall might, perhaps, be rekindling things with Devin once again -- whom she broke up with almost 2 years ago -- after her latest romance with Benito.

The interesting thing, of course, is that Kendall was recently spotted hanging with Bad Bunny after their own split a couple months ago. Remember, they'd been seen running with the same crew to ring in the New Year ... and some thought they were getting back together.

If she's chillin' with Devin, though ... that now seems unlikely, especially with BB there in Vegas, but nowhere near her. From this -- you can kinda assume ... they're probably over.

Devin was Kendall's previous boyfriend before Bunny ... so, retracing her steps a bit.