Connection: USG Fiber --> SFP+ to unmanaged PoE switch --> U6-Pro

U6-Pro has a 1GBE connection to the non-unifi switch, but unifi gets confused by that:

Port Manager:

Access Point:

Network Optimizer:

My suggestion would be to trust the device above the port manager :-) Also, you could build in a logic check if speeds are higher than its HW capabilities.