Having an empty USB-C-to-A adapter anywhere disables USB 4

[Malstrond]

Hi everyone,

I'm connecting an Acasis TBU405 USB 4 NVME enclosure to my M3 Max MacBook Pro. It uses an Intel JHL7440 controller for USB 4 and a Realtek RTL9210B for USB 3.

It works in USB 4 40gbps mode - but ONLY if there is no USB-C-to-A adapter anywhere else on the system.
As long as such an adapter is plugged into any port, even if the adapter is empty and not connected to anything, the Acasis enclosure only negotiates USB 3.1 10gbps mode.

I even tried connecting a hub with a native USB-C connector (Anker PowerExpand) - which has no detrimental effect. But If I plug the empty adapter into the USB-C port of that hub, the enclosure once again doesn't work in USB 4 mode, even though it is not connected to the hub at all, but to a different port directly.

I also tried adapters from 5 different brands - all cause the same problem.

But if I connect the enclosure first and then the adapter, the enclosure stays in USB 4 mode and works at those speeds.

This is magic switch levels of strange. Has anyone ever seen this behavior?

 

[Fishrrman]

What kind of USBc-to-USBa adapter are you using?
Could you give us some actual examples?
Are we talking cable adapters like this:

Or... something else?

I'm thinking an adapter like the one pictured above is "dumb" (i.e., no electronics inside, just a physical "swap" of connections), but I could be wrong. Wondering how that could affect things?

 

[Malstrond]

(i.e., no electronics inside, just a physical "swap" of connections), but I could be wrong. Wondering how that could affect things?

Exactly, that's what I'm wondering.

All of these cause the same issue:

 

[Malstrond]

In the end, this problem was unsolvable.

I tried various different enclosures with Intels JHL series controllers. All of them exhibit the same problem as long as an empty USB-C adapter is plugged in.
My workaround was buying a different enclosure, one with an ASMedia ASM2464PD controller (for example ZikeDrive Z666).