I see, thanks for the explanation. So basically hardware modification would be required to make full use of this cat. 12 modem. Weird design choice IMO. @josepc, do you have 3CA thanks to a 4x4 MIMO antenna as well?
I am not using any external antennas. The chateau LTE12 includes 4x4 MIMO internal antennas
In this case, considering the fact I'm not using an external antenna right now, I should be getting 3CA - unless my ISP is in fact not supporting it/blocking it, I have asked them about it yesterday and I'm waiting for an answer.
On one side, I wish I had learned sooner that MIMO impacts carrier aggregation directly, before I decided to mount the antenna I purchased... On the other hand, considering the prices of 4x4 MIMO antennas and the fact that messing with the internals of the router would be required, I'm thinking I'd give it a pass anyway, and settle on 2xCA with an external antenna instead.