I also logged in to dropbox website, and removed from security the "old" version of the computer and logged in with the new setup to see if there is a difference. But no.
I have dropbox plus account, so I´m not limited either by hardware amounts available for me. In the meanwhile, in the same network I use, all the other devices sync normally.
So, I wonder why syncing fails. The dropbox does not give me error message of any kind. It just has the blue sync symbol there, but no files are downloading from the cloud to my computer. My settings allow downloading of nearly everything back to my computer, just skipping one large video folder.