Hi Mihai Bejgu,
Have you went to the Salesforce tab in Admin and checked the last time the sync happened? See picture below. I would start there and then would check with the Salesforce admin to see if changes were made on their side around the time of the last sync.
I would also check that the Sync user is still set up correctly. Maybe someone did a clean up and deleted the profile or changed the settings. The fact that you are receiving no notification leads me to believe that the connection between the two systems is broken as if they were still connected you would be receiving sync errors from Salesforce, or that is what I would expect to see anyway.
There is a full list of documentation on the sync in the Marketo Docs Step 2 of 3: Create a Salesforce User for Marketo (Enterprise/Unlimited) - Marketo Docs - Product Docs
Thanks Gerard. I managed to isolate the problem with your suggestion.
Great! Glad you got it sorted.