according to the user connected, Zabbix front-end latency changes dramatically!

After lots of tests, I tend to relate the latency with the complexity of the permissions for the user:
The speed for a super-admin with all authorization is high while the latency is greater for a user with complex restricted permissions.

Is it a known issue in Zabbix?

Is there a way to improve this performance problem (index in DB or something)

Thank you in advance,

Simon