Hard drive malfunction? USB port malfunction? Or just normal?

I recently purchased an HP ProBook 450 G3. I am using two passport compact 1 TB drives with my laptop's two USB 3.0 ports. In normal use there is no problem. However, when I copy a lot of data from one to the other (or from one to the laptop's internal drive) the drives keep disconnecting. I know this because first I will get a copying error saying either the source or the destination is missing. Then I will hear the "chime" that Windows makes when a USB device connects or disconnects. Then the autoplay window for the Passport drive will appear. It seems that it spontaneously disconnects and then reconnects. I can continue using it for a time afterward, but it always spontaneously disconnects at some point, always when I am doing large data transfers.

I wondered if I have a poor physical connection---the USB plugs seem a bit loose. I checked if there is any vibration or movement that could break the connection, but so far there is no evidence that anything is moving. The disconnection always happens when a lot of data is being transferred, while the drives are sitting completely still.

Any ideas how to debug this?

This is a hard situation to diagnose from a distance IMO. "Loose" is somewhat subjective, and barring serious abuse the only kinds of usb connectors & ports I've ever seen fail mechanically are mini and micro USB2 types.

I'd be inclined to suspect the drives first, especially if they are from the same family and were produced around the same time (the "bad batch" phenomenon). Have you tried to reproduce the problem on other machines, or with different drives on your machine?

I also have two passports and the same thing happens to me. I have no proof of this but I always felt it was to much of a drain on the power supply with both passports plugged in at the same time.

What I do if I need them both plugged in is use a POWERED usb hub. The hub will get its power from your house current and not the USB port on the computer. When I use the hub, I don't run into this problem. With just one drive plugged in I can transfer files all day long and I don't need the hub.

I will have to do some debugging to see if it happens with one drive only. Maybe it is always the same drive causing the problem and the other one is fine. I will check transfers to/from the laptop's internal drive also.

I found a good way to debug. I'm using SyncToy. This is better than copying and pasting in Windows Explorer. The reason is that SyncToy will process files that need to be moved, and if some fail, it just keeps going and provides a report at the end of which copies worked and which failed, so I get a sense if the drive disconnected/reconnected just once, or many times, or something in-between.

I'll report back.

I use a similar program called HashTab. Before it starts transferring files, it creates a hash of the files you want to copy and then creates another hash when it's finished. It then compares the two. It's similar to sha1. It lets you know if they do or don't match.

It doesn't seem any slower than file explore but even if it was, I care more about accuracy than speed.