Freenas 11.2 U2.1 abysmal gui / system performance

Hello,
i'm running Freenas now for more than half a year in preparation to make the migration away from Unraid.
Specs:
Intel(R) Xeon(R) CPU E3-1231 v3
Supermicro X10SLM-F
32GB ECC

I have 2 pools:

Mass Storage 14x4TB Raidz2
SSD Pool 3x240GB Raidz1

Boot drive 16GB USB3.0 / 64GB SSD SATA (upgraded from USB stick yesterday fresh install)
The boot drive and the SSDS are connected to the onboard SATA.
HDD pool is on a LSI HBA IT Mode

Now i migrated all my stuff over and the performance is...

Freenas 11.2 U2.1 abysmal gui / system performance