You can temporarily remove the usb_sharing.sh script, though that'll come back when Steam Link is updated.

Can you provide instructions on setting up usbip so I can reproduce this here?

Unfortunately, removing the usb_sharing script did not solve the issue, even temporarily.

The way I have usbip set up is with a controller(s) connected to a Pi Zero 2 W via USB and a Pi 5 with the SteamLink client, both connected to the same LAN.

I created a service on each end to initialize everything on boot, but you can get it going temporarily without all that.

As root or using sudo, on the remote/server device, install usbip, then run "modprobe usbip_host". "usbip list -l" will give you a list of available devices. It may look something like this:
- busid 1-1.1 (045e:028e)
Microsoft Corp. : Xbox360 Controller (045e:028e)

- busid 1-1.2 (045e:028e)
Microsoft Corp. : Xbox360 Controller (045e:028e)

Bind a device using "usbip bind -b 1.1-1", for example.

On the device with SteamLink, again install usbip and enable the client using "modprobe vhci-hcd". Attach one of the remote devices using "usbip attach -r usbservernameorIPaddress -b 1.1-1". The command "usbip port" will then show you something like this:
Imported USB devices
====================
Port 00: <Port in Use> at Full Speed(12Mbps)
Microsoft Corp. : Xbox360 Controller (045e:028e)
5-1 -> usbip://piusbserver:3240/1-1.1
-> remote bus/dev 001/054

I'm then able to use the USB controller attached remotely to play games on RetroPi/EmulationStation without issue. When I open SteamLink, however, it shows no controllers found and, after exiting SteamLink, reentering the command "usbip port", I get:
Imported USB devices
====================
with nothing following and have to unbind/rebind the controllers from the server before they can be reattached on the client side.