Can't add data even with the righ autorizations

Hello, 

I manage a team of 6 peoples working on a data base to organize their task.

Each collaborator have theur own Kanban view like this : 

I don't know why but since 1 week my new collaborators don't have the bue cross to add a new task. 

They are all editors and they can edit other bases and other tabs but not this particular tab. 

Can you help me ? 😁