I want to thanks everybody for all the answers.
Final cut works better now!
I started to open a new project, copy/pasting only the sequences I needed but I still had problems.
I tried many times to uppgrade to the decklinks latest driver but there was a problem unzipping the
7.9.6 driver FROM: https://www.blackmagic-design.com
But yesterday I noticed that a new driver was added on the page so after installing the 8.0 DRIVER everything worked fine again.
Today I feel like a happy new born editor so once again thanks everybody!