> it HAS to work behind a hub
I tried to connect my UFX+ behind an USB3 Hub which is connected behind a 4x USB3 controller with FL1100 chip. It works. So one can not say generally smth like this wouldnt work.
Ok then you need to find out what triggers the issue.
1. test whether the UC alone has a chance to work behind the HUB, from that I read this you didnt test
but this should be the 1st test IMHO to find out, whether there is any potential chance, whether
the UC can operate behind the HUB.
When this works then you need to find out, which other device or combination of devices might cause issues.
Simply connect the 2nd, 3rd and 4th device ALONE together with the UC (so that only 2 ports of the HUB are in use)
to see, whether each of those are capable to work together with the UC behind the HUB.
In a good case of look you can quickly find out which device might cause issues.
If this doesnt trigger the issue you need to find out, what combination of devices cause the issue.
Maybe you can replace this device with another one which has another driver and by this behaves differently on the bus so that at the end everything has a chance to work.
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13