I initially looked at the sender name and actual send time and when I didn't see anything fishy there I moved it to the email people. Sorry I didn't follow up. It may take time to find the source of the problem so don't hold your breathe. ;)

The problem may be that your email provider didn't release the email to you until the next day, which is one usual culprit. I use to work for the email team, but now I'm in planning. I'll let you know when I hear something. In the mean time let us know if you receive the other email late, forward it onto me again and we'll add it to the ticket.

I've had the check-in e-mails arriving several hours after departure as well...

Haven't received the other email yet. My provider does have a quarantine area for suspicious emails, but nothing from Frontier has ever appeared there. It does appear odd that F9 would be the only airline that can't get an email through - no problems with UA, DL, AA or US - so that would indicate to me a problem originating with F9.

MostlyAir confirmed today that it's a problem with check-in emails not getting sent to the email provider in a timely manner, and it's affecting more pax than just me. He's a great example of customer service in a world where it's vanishing all too quickly.

Customers are complaining about the website's search engine timing out, but it's obvious that the problem occurs when searching for an itinerary where at least one of the segments involves a discontinued route/market. Since many of the soon-to-be discontinued routes and markets are still viable for at least another month, it's probably a challenge.

They need to program the system so that instead of it searching endlessly and timing out, a message pops up that there is no service available for the XXX-XXX part of the itinerary, for the dates being searched.

Seems an old error is happening again.
 

Seems an old error is happening again.

Wrote Frontier Airlines and they are denying any issues and blaming the customers.

The fare you were searching for is either no longer valid or the fare availability has changed. Please click Start Over to try your search again.

Trouble booking to AZ
 

Can't book any flights for any times to AZ

The fare you were searching for is either no longer valid or the fare availability has changed. Please click Start Over to try your search again.