Your Elements Connect fields configured with an LDAP datasource fail with a similar error:
This error is returned by your LDAP server, that means the problem seems to be outside Jira actually. LDAP error codes are always explicit, in your case, here is the meaning:
LDAP: error code 4 - Sizelimit Exceeded:
LDAP Server settings. There isn't a universal way of solving this problem, for it depends on a number of reasons: what kind of server you are working with, whom the server belongs to, whether or not you enjoy administrator rights and physical access to the server. If your server is absent in the list of solutions recommended for well-known servers, we suggest you ask your system administrator or consult the server documentation.
Workaround for well-known servers:
Microsoft Active Directory. By default, Microsoft Active Directory which is a part of Windows 2000 Server, allows fetching only 1000 entries per one search request. In terms of this system such a restriction is called MaxPageSize. This parameter can be changed using the ntdsutil.exe file which is a command line tool supplied with Windows 2000 Server. Another way to change this parameter is to edit it directly inside the CN=Default Query Policy, CN=Query-Policies, CN=Directory Service, CN=Windows NT, CN=Services, CN=Configuration, DC=YOUR_COMPANY, DC=YOUR_COMPANY_TLD entry by using LDAP Administrator. In both cases you must have administrator rights.
OpenLDAP. The time limit for the OpenLDAP server can be changed in the config file (which can usually be found at /etc/openldap/slapd.conf). The parameter is called sizelimit. For more information please consult the slapd.conf Manual page or the OpenLDAP documentation.
This issue originates from the LDAP server, please contact your LDAP administrator.