USB 3.1 Gen 2 drops to 5Gbps on M1 Mac mini

I recently replaced my 2018 i7 Mini with a new M1 model. One peripheral I had attached to my "old" Mini was a 2-bay USB 3.1 Gen 2 enclosure with two SSDs in it, striped for speed. (Redundancy isn't an issue for its function.) Like on the i7, the enclosure is directly attached to the M1 Mini.

After Blackmagic released their new version of the disk speed test, I did my usual benchmarks of my drives to see how they perform. I was surprised to see the enclosure report back about half the speed it usually does (around 400MB/s as opposed to 850-900MB/s.) Fearing some sort of issue, I ejected it and connected it to the late 2019 16" i9 MacBook Pro I use for work. Just as on the Mini, it's directly connected. On that machine, it ran as expected. A bit more looking with the System Profiler shows that on the M1 Mini, the link speed to the enclosure is 5Mbps, while it shows up at the full 10Mbps on the MacBook Pro.

After doing some searching around, I see that others have seen this issue with the new "USB 4" equipped M1 Macs. (I use the quotes because the USB specs are a nightmare these days.) However, as murky as things seem, from what I can read the ports on the M1 Mini should support USB 3.1 Gen 2 at the full 10Gbps speed.

Am I missing something? Losing that much speed on a 2T external drive really hurts. Is this a bug, or the result of some confusing statements by Apple?