The sensor report shows the wrong fan headers for the Gigabyte Aorus Z390 master MB. Here is what I was able to determine on my MB fan headers. I did not use System 1 fan header and since AIDA64 did not see a Chassis 3 fan sensor I have to assume that System 1 fan header is your Chassis 3.
CPU = CPU
CPU OPT = System 6 Pump
Chassis 1 = System 3
Chassis 2 = System 2
Chassis 3 = not reported
Chassis 4 = System 5 Pump
Chassis 5 = System 4
Chassis 7 = CPU_OPT