Okay, so I did some more extensive testing to try to find the source of this problem. I create two clean accounts, on the first one I copied Application Support from my main user Library, and on the second I copied the preferences folder from the library.

On the first account all my utilities get open at login, and AutoCAD works as it should.

On the second account, the one to which I copied the preferences folder, presents the panning issue. So there might be some setting in some app that interferes with AutoCAD. Just to be sure, I deleted all contents of the preferences folder, log out, log in again and... the problem is still there. So piece by piece I nuked the whole Home folder of this test account, just to find out the problem persists. Whatever is triggering it from my preferences folder, it is permanent.