If the CSPGatewayLatency is almost 5 seconds -- ignore, this is false positive, fixed in 2024.1.2. Or better -- upgrade! ;-) https://docs.intersystems.com/iris20241/csp/docbook/changes/index.html#CSPServer_DP-433569

No.

You can filter results based on the row level security policy Row-Level Security https://docs.intersystems.com/iris20252/csp/docbook/Doc.View.cls?KEY=GOBJ_persother_rls#GOBJ_persother_rlssetup

You can also grant access to specific columns in tables to particular roles, and then grant these roles to a particular user https://docs.intersystems.com/iris20252/csp/docbook/Doc.View.cls?KEY=RSQL_grant#RSQL_grant_synopsis