I have a couple of new external USB 3.0 enclosures (UGreen 30848 and StarTech S251SMU33EP) containing SSDs. Using the R5E with X99 chipset the connection to mobo USB 3.0 ports are unstable and keep disconnecting, if they are recognized at all. If I plug them instead into my add-on USB 3.1 (10 Gbps) ports on my PCIE cards, they connect stable and work fine. Any ideas?

I wonder if it is because these external enclosures support UASP (USB Attached SCSI Protocol) for extra speed, and maybe the mobo USB 3.0 and drivers are too obsolete to play nice with UASP enclosures? In Device Manager under "Storage Controllers" they appear as "USB Attached SCSI (UAS) Mass Storage Device" when connected through the USB 3.1 PCIE cards.