Naming series stop working

customer’s naming series no longer works.
the new customers are not named. I set the namig series both in the customer doctype and in the settings but nothing works.
I’m not the only one using the system but other users just insert new items.
before customers were nominated with the MC-CL.YY.####. series and everything worked beautifully.
Since yesterday when I create a new client he just doesn’t take the name of the series and the space where it should be written remains empty.