That’s not a common occurrence. Points and $ does not necessarily = ticketing unfortunately. And if partner airlines are involved it can get complicated.
Would be interesting to get the full details.
I've had this happen on a number of occasions in the past 6 months. All with Qatar.
Here are the times it happened, and the reasons.
1. Qatar auto cancelled a AMS - DOH - SIN part of my award booking due to removing all Singapore transits and putting in the requirement for Government approval because reinserting all the flights. They removed my flights, then reinserted them into the booking - Same flight numbers and times, but with a warning about the transit not being approved (this is what the Qantas call centre in Hobart told me). This booking was Auto-Cancelled because Qantas didn't
re-ticket the booking after the changes. My e-ticket, that had been ticketed for 6+ weeks, had the exact flight details but Qatar would not honour it. Qantas put me in revenue full price J to try and avoid this happening again...
2. Qatar cancelled the same part of the same booking due to the DOH - SIN being a revenue booking but the rest being a Oneworld Award. Qantas couldn't help, and there were no award seats left anymore. This happened weeks after receiving my new e-ticket and re-selecting seats.
3. I then rebooked via Hong Kong (before the ban on flights). Qantas didn't re-ticket the booking in time. Auto-Cancel.
4. I was lucky my seats were still available, Qantas ticketed the booking again while I was on the phone. Happy days. Qatar made a schedule change 1hr earlier, also using the Cathay Pacific 777 instead of a Qatar A350 for DOH - HKG. This was auto-cancelled because it wasn't re-ticketed.
This is where I gave up on using Qatar in my booking. There's only so many hours I can spend trying to rebook the same flights I have already had ticketed.
Yes they were all originally ticketed and seats selected, except #3, but were cancelled anyway. I never got a notification, I only saw the change because I was logging in daily to check for a better routing. I wonder if could have turned up at the airport in May and found out at Check in that my flights were gone if I didn't obsessively check things.