So I had an older Elgato TB2 hub lying around and wanted to connect it to my 2020 Intel high-end 13" MBP. I found an Apple TB3-TB2 adapter in a drawer and hooked it up.
I started by using the MBP’s port closest to the edge (farthest from the trackpad) on the left side. Nothing. Disconnected hub, reconnected, still nothing. Power cycled the hub. Still nothing. Not even a USB KB connected to the hub worked. Hub works just fine on an older MBP so I know it’s not the TB cable. Anyway, Sys Profiler showed nothing attached. So then I switched to using the other port, the one closest to the trackpad and presto everything worked as you’d expect.
Due to the way peripherals are connected to the hub (and the silly short cable) I only tried the ports on the left side of the MBP. So my question is, is there some kind of known limitation of the TB3 ports on this MBP where only some work with hubs, or is this an indication one of my TB3 ports is wonky? Admittedly, I otherwise usually only use that port for charging so I have no idea if USB peripherals work on it. Hardware diagnostics reports nothing though for whatever that’s worth.
Ha, I knew somebody here would have an idea. Thank you, @tommy.
I actually did not. Are you talking about rotating the TB3 end of the adapter in the MBP’s port? The rest of the chain is TB2 and that is unidirectional. Or did you mean rotate the TB2 cable (between dock and adapter) so the end that’s in the TB2 dock goes into the adapter and vice-versa?
Well the first option really but when it comes to all things TB and USB-C I’d flip it every which way until it worked. I have taken to marking with a dot indicating “This side up” with Sharpies on those cables.
I was mainly curious if I was alone in tripping up using them.
I have also found that power considerations vary widely decide to device.
So today I got my hands on that old TB2 dock again and this time I plugged in the TB3-TB2 upside down compared to last time. Voila, it worked right away. So I turned it around again (so now TB symbol facing up again) and it still worked. This was on the same port (left side, back port, i.e. farther from trackpad) I couldn’t get it to work last time. ???
The only thing I can think of that might have changed is that the MBP had been rebooted in the meantime for the 11.5 update.
I’ve wondered if it is that, possible for sure but I’ve had similar experiences and I’ve just ended up viewing those interfaces as a tad unpredictable.
I’ve an unpowered USB-C hub from Anker, one of those ubiquitous 7-1 types, hanging off a TB3 port on my iMac. The SD slot won’t work on it. It does when the hub is attached to my MBPro.
I tried it several more times later on and it always worked on either port. That TB2 cable is high-end and has been in use in various setups and never gave any trouble. The adapter rarely sees use, but it’s straight from Apple, no reason to doubt it. I suppose it was simply the reboot that managed to rejiggle things just enough to get both ports to work again. If the setup were more flexible (physically) I would have also checked out the right side ports just for fun.
Anyway, indeed a bit unpredictable. A shame considering all of the hardware involved is fancy stuff. But not really a big deal either. It shall remain a curiosity.
Thank you, 
