I have researched it to death... and tested it with a wide variety of new and old enclosures with and without powered & unpowered hubs myself and am nearly completely confident this IS a macOS bug and not all of the redirects that tend to get slung when this topics comes up (firmware, cable, hubs, user error, settings, etc). Too many people, with too much differing equipment, etc are suffering the problem (but not everyone of course). The most telling in all of the research was with many people upgrading from pre-Big Sur to a newer version of macOS, crashing into the problem with their enclosure(s), then- needing the stable enclosure more than the update- downgrading and the enclosure works fine again. To me that screams where this problem lies because everything else remains the same.
I've got an important RAID enclosure forced retired because it can't keep its connection... unless I take it to any older Mac and then it is as stable as it can be. It is very frustrating that the "just works" company can't resolve this bug over now nearly 4 generations of macOS.