G-mail Account Disconnecting All the Time - Emails not working on boards for a user

One of my users is constantly disconnected or/and the emails automatisations just do not work for him. We reconnect him, they work for the next client that arrives on his boards and then the clients after him - no results. I checked the admin on gmail, I whitelisted the IPs, I recreated at least two times all the automatisations and the email integrations for him from A-Z by deleting the email, reconnecting it, connecting it, etc, nothing works fine.