Dock D600 not recognizing USB 2.0 devices

Hi,

My Dell D6000 dock is not recognizing any USB 2.0 devices, such as mouse, keyboard, flash drive etc. It's working fine with USB 3.0 devices and has power in the ports to e.g. charge a phone. Initially it worked also with the USB 2.0 but at some point it stopped, so my guess is that some update ruined it. Any of the 4 ports doesn't work so physical damage can be ruled out. 

I've updated drivers (system says I have the latest ones) and also tried to update or downgrade FW but at that point the FW updater does not find the D6000 saying "Please connect D6000". I've tried it several times on two separate laptops, with and without any devices connected to the D6000, through type A and C ports. Nothing worked. 

Please help.