A few questions...
- Did your OS report I/O errors, or did you get silent data corruption?
- What's the interface on the dock - USB 3.x or something else (e.g. USB 2.0, eSATA)?
- If the interface is USB 3.x, what's the chipset on the USB 3.x port you're plugging the dock into?
- Have you tried a different and/or shorter USB cable?
- Were you hot-plugging drives?
A few general observations based on my own experience with dual drive docks:
- 3rd party USB 3.x chipsets on some motherboards can be hit or miss. Use a port that is native to the motherboard chipset if possible.
- Try connecting to a USB 2.0 port instead. Yes, it'll be slow; but it'll allow you to determine whether the issue is with the USB 3.x interface.
- Dual drive docks generally don't like it when you hot plug drives if you're using both slots.
- eSATA based dual drive docks are hit-or-miss because they use something called a "port multiplier", and there are multiple standards for how to implement port multipliers. If the dock's port multiplier flavor doesn't match what the SATA controller supports, you're SOL.
- I've had better luck with Vantec, but none of them have been 100% trouble-free. You probably want to avoid ThermalTake.
- If you're dealing mostly/only with 2.5" drives, you may want to consider a couple of these instead: https://www.amazon.com/gp/product/B00HJZJI84/