These are some screenshots , and request/response when I disable second instance in in LDAP Authentication and Lookup 0.6.2 plugin and can add collaborators successfully.
Request URL: http://helpdesk.mydomain.com/scp/ajax.php/users?q=kanel.khanh
Request Method: GET
Status Code: 200 OK
Remote Address: 192.168.7.4:80
Referrer Policy: strict-origin-when-cross-origin
Cache-Control: no-store, no-cache, must-revalidate
Connection: Keep-Alive
Content-Type: text/html; charset=utf-8
Date: Fri, 02 Dec 2022 02:04:45 GMT
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Keep-Alive: timeout=5, max=97
Pragma: no-cache
Server: Apache/2.4.37 (centos) OpenSSL/1.1.1k Phusion_Passenger/6.0.7 mod_perl/2.0.12 Perl/v5.26.3
Transfer-Encoding: chunked
X-Powered-By: PHP/8.0.24
Accept: application/json, text/javascript, */*; q=0.01
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9
Connection: keep-alive
Cookie: OSTSESSID=n2n41325rpntnruo905mpdavds
Host: helpdesk.itl.com
Referer: http://helpdesk.mydomain.com/scp/tickets.php?id=18338
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36
X-Requested-With: XMLHttpRequest
Response
[{"email":"kanel.khanh@mydomain.com","name":"Kanel Khanh","info":"kanel.khanh@mydomain.com - Kanel Khanh","id":1069,"\/bin\/true":"kanel.khanh"}]