Was on 1852 last night. Interestingly, it was still showing a 321 (with 16 J seats) until after the scheduled inbound (1851) was delayed. It looks like, from watching the app, that 1851 needed a new aircraft (just like it did when I took it down to Vegas on Monday, although that time it was a swap from a 12J 321 to a 16J 321) and a 320 got the job.

Needless to say, we left some folks behind, who maybe (hopefully?) got the redeye home instead.

1852 ended up being quite late, and then we waited about an hour to get a free gate. Ended up getting off the plane four hours behind schedule -- an improvement over the 4.5 on the way down.

At least Nexus customs was quick and painless at that late hour.

But it makes me wonder. It sure looked from app-watching (AC app, FR24) that they were planning on yesterday's 1851 to be a 321, right up until it hit delays. Then it got switched to the 320 that ultimately flew it. But then, OP being proactively rebooked suggests they knew something was up a couple of days in advance.