Canadian Passport Issue

On August 26/22, we flew from Guadalajara to Calgary on American Airlines and returned on September 26/22. Before we left Ajijic I checked in on-line with no problems. However, when I tried to check in on-line for our return flight, I rec'd a message advising 'unable to check in on-line. Please check in at the AA desk'. Turns out the reason was that my passport expires in less than one year. We were travelling in September, 2022 and my passport expires in August, 2023 - 11 months validity, but still less than one year. I always thought there must be at least 6 months before expiration, but maybe things have changed, or maybe this was just a one-off.

I thought it was six months as well.