Since I don't see an Aeromexico forum, and this was booked by Delta.com, I thought I'd post here.

So this was my first time flying Aeromexico that was booked from Delta.com (First class)
1/14/19 - SJD -MEX (Aeromexico
1/14/19 - MEX - ATL (Delta)
1/14/19 - ATL-ALB (Delta)

I get the delta app that tells me I'm ready to check in, I click the links, it tells me I need to use Aeromexico to check in because the first flight is operated by them. OK, no issues, it redirects me to Aeromexico's website, which finds my information and asks me to enter my passport info, emergency contact, and I check the box stating I'm not transporting prohibited items.
Then everything falls apart (tried an actual PC with a different browser as well).

The "continue" button is grayed out and when I try to click it, it highlights the Global Entry/KTN box (which is under the "optional" section) in red, stating that I've not entered my CBP information.

Well I don't have Global Entry, and 2nd it's optional (according to their website). So no checking in ahead of time.
They must've had a problem because at SJD I checked in OK (supposedly) but they called me and about 5 other passengers at the gate and wanted my passport again and had to re-scan into the system for some reason.

The flight was an ancient 737 (800??). Like with the two buttons (one to recline another to chop off your feet with the foot rest that you can't possibly use unless you're maybe 4' tall). Wi-Fi wasn't working, and neither was the inflight entertainment system.

Crew was courteous, we had the choice of a small muffin or a small roll of some sort and water/juice and that was that.

When I went through MEX, they apparently had to re-scan my passport yet again (and by re-scan I mean they swiped it several times to read the number to put it into the system) (not sure what was going on) and re-issue boarding passes for some odd reason, but fortunately after that things were fine.

Not sure if this was a bug on Aeromexico's website, or if that's how it normally works (you can't check-in unless you have Global Entry), but I found it odd.
Not impressed at all with the First class cabin or the plane, as I'd kept hearing how nice Aeromexico flights were in First, so it was a bit disappointing. Although at least the crew smiled and was pleasant (unlike a certain other AAirline-LOL).