3817100 - Why is stored fare getting updated from FLEX to TANGO fare by Concur on Air Canada in Apollo GDS?

I had booked my Air Canada flights in Concur and chose a Flex fare.  My trip was placed on hold and I later went back to change my trip.  When I confirmed the changes, the fare was no longer a Flex fare but a Tango fare.  Why did this happen?

Traveler books Air Canada, branded fare FLEX, but the traveler makes a change to their itinerary and the stored fare is updated to a lower Tango fare , KBA , CON-CA-ADM , Administration , CON-CA , Cross Applications , CON-SRV-TRV-ADM-LAN , View Airlines , Problem