An issue does not get synchronized and appears in the troubleshooting section with the category 'Field not on screen' and a message containing, e.g. '"customfield_11200":"Field 'customfield_11200' cannot be set. It is not on the appropriate screen, or unknown."'.
The 'customfield_11200' part identifies the internal id of the field which is affected.
A change occurred in the sender project and the field which is being sent to the receiver project is not on the corresponding edit screen or transition screen (if a transition is configured for performing the changes).
The following steps should be done in order to resolve this problem.
Check if the field is defined for the corresponding screen of this project.
Alternatively use the JIRA admin helper to identify the problem.
Access the Field Mappings configuration and make sure that you chose the right fields for your configuration.
After fixing your configuration...