Weird issue with Lian-Li UNI FAN SL120 Infinity and L-Connect 3 Controller — PWM not adjustable when USB is connected

Hey everyone!

I’ve run into a strange issue with my setup and wanted to see if anyone else has experienced this.

I’m using 6 Lian-Li UNI FAN SL120 Infinity fans connected to the Lian-Li L-Connect 3 controller (UNI HUB). I also have the RGB headers from my custom water cooling components plugged into the hub.

Here’s the issue:
When everything is connected — including the USB cable from the UNI HUB to the motherboard — the fan RPMs are detected correctly (both in BIOS and Windows), but I can’t control or change the PWM curve at all. They just run on default speed I guess. BIOS curves don’t work either, and manual control does nothing.

However, if I disconnect the USB cable from the controller, PWM control starts working immediately — BIOS fan curves apply as expected and I can change PWM manually in Windows.
But then the downside: RGB lighting doesn’t work after reboot without the USB connection.

I’ve tried multiple Lian-Li controllers, and the result is always the same.

Has anyone dealt with this? Any solutions or workarounds?