XPS15z USB 3.0 ports and Drobo 5D

Hi.

My (very expensive) Drobo 5D external "beyond RAID" drive won't mount first time on my XPS 15z (upgraded to W7 Pro 64-bit) using the USB 3.0 ports.

Mounts, then disappears. Then have to reinsert USB 3.0 cable and it finally mounts properly and drives show green in Drobo Dashboard (yes, latest version). Sometimes dismounts again and regularly doesn't shut down properly. Will run on USB 2.0/eSATA port.

Been through several suggestions from Drobo. Have updated all drivers but still no joy. Drobo works perfectly connected to wife's W10 64-bit laptop.

No other devices seem to have same problem using USB 3.0 ports.

Any ideas?

Alan