Steps to reproduce:

1. Install zabbix mysql server on ubuntu 20.04
2. Import Template "customized" to add token authentication and real URL link
   1. Made from : https://git.zabbix.com/projects/ZBX/repos/zabbix/browse/templates/app/gitlab_http?at=refs%2Fheads%2Frelease%2F5.2
   2. default token anonymised
   3. added to request
3. Associate to the gitlab vip or host
   1. fille the URL, TOKEN and PORT macros as wanted
4. Try to test the the 3 metrics polled by Gitlab :
   1. it works for "GitLab: Application server status" and "GitLab: Instance readiness check"
   2. it doesn't work after 66108 caracters (bite vs byte we can imagine 65535) for "GitLab: Get instance metrics"

Result:
Json not parsed after 66108 caracters, See screenshot
Expected:
Check for not supported value or/and Prometheus to JSON preprocessing steps to accepte more than 66108 caracters from /metrics