Please note that during demanding use-cases the Thunderblade enclosure will heat up. This is expected — the case is designed to act as a radiator, drawing heat away from the internal components. Because of this, we do not recommend stacking multiple Thunderblades, as the combined thermal effect may cause one or more of the devices to stop operating normally.
If you already have two or more drives stacked together and notice erratic behavior, the best thing to do is save your work if possible, stop any active transfers, then unmount the drives from the system and physically separate the drives so they can cool off. After they are cool you can reconnect the drives to the host system (leaving them unstacked) and they should operate normally, without further interruption.