I posted this in another J3i Forum thread, before I saw this one -
I received my Fusion Flex J3i on Tuesday, as well, and installed 2 SSD drives, and one HDD, with one of the SSDs connected to that internal USB port.
The problem is that the drive that's connected to the USB port randomly gets connected a couple of times a day, and I don't why it's doing that. I keep getting the "drive was ejected improperly" or something along those lines error message. Obviously, I need something more reliable than that, so I'm hoping it's a bad cable? Maybe the Mac Pro needs a firmware update? Not sure. There was ONE instance of all three drives disconnecting, but that was after waking it from sleep - again - not good. But if it's a matter of just not having it sleep, I can live with that for the time being.
I've had that drive for over two years. I swapped out that SSD for the other one, to test a different SSD connected to that same internal USB port, and the disconnects happened with that SSD, too.
I reset the SMC, but that hasn't helped.