error code : 30220

Hi,
I randomly get the following error message: error code : 30220 error message : Le numéro de portable du destinataire n'a pas été transmis.
The phone number is required and should always be filled in.
I noticed that the field is not always displayed but in this case, it usually get the phone number from a cached value or something (?), and my issue does not seem to be related to this behaviour.
Any idea ?