While not explicitly on CX (this was SQ), I had a similar occasion where I had cancelled my old AMEX and replaced it with a new AMEX. Both were charge cards and obviously registered to myself so they had similar numbers including the same last 5 digits but obviously the entire number was different.

In anticipation of such similar problem, I emailed SQ after I got my card informing them of the situation and whether it would be OK to discard my old card or not. They gave me the OK to discard so I happily went to the airport, only to find out that when my new card was swiped at check-in, the system obviously didn't like that.

Luckily, I had the email from SQ saved on my phone to show the check in agent and we just had to go over to the service desk which was immediately next to the F counter and had the supervisor 'override' the system.

Still, I was thinking it would've been better if I had kept the old card.