Hey! I had exactly the same experience today!

Tried to upgrade myself for DOH-CGK leg of my flights. Was told at the Platinum Lounge that the upgrade will cost me either 39 Qcredits OR 94,500 Avios, which I found was shocking. On the "My Calculator" page, an upgrade from Economy (booking class O) to Business Class would cost me either 39 Qcredits OR 63,000 Avios.

The staffs literally had to call several people because they also found it confusing but in the end told me that unfortunately they have to go with whatever number is shown on their system at the airport. Unfortunately, I had to choose using Qcredits because at least that one went accordingly to the "My Calculator" page unlike Avios.

It's striking to me that our issues are exactly the same: the Avios required at the airport is 50% more than what's shown on "My Calculator."

Even weirder, the day before, I upgraded myself online using Avios as well (MAD-DOH, DOH-MAD) and those went without problems, each leg requiring 40,000 Avios (just exactly according to the website). So maybe it's indeed a new policy for Qatar Airways to charge more Avios on "last-minute upgrade" at the airport.