For me it is the first time to hear of such a behaviour. Does the PowerBlock work fine afterwards or has it become just unreliable at all?
Maybe there was some sort of voltage transient that caused the malfunction of the PowerBlock IC.
Hello, we recently identified a bug in the ControlBlock driver. I am very sorry for that!
Your observations see to match the symptoms caused by that. We released an update yesterday and that should also fix your problems.
The power switch on the ControlBlock lead to a small voltage-drop at the switching component (as does every electronically component). From other projects I know that especially additional USB devices can be problematic. I guess that when you disconnect, one or both USB devices (SSD, converter) the under voltage disappears. Alternatively, you could get an active USB hub that powers the additional USB devices and keep the connection between the RPi and the USB devices.