Hello Dominic
I have the same cable. I only use one, but the connection works for me without interruptions. (Use it between the screen and a Surface docking station).
Regarding your described problem, I would rather conclude a problem with the connector. Either they are not plugged in nicely/correctly, or they have a loose contact.
That depends on the Samsung monitors. Do they have Displayport or HDMI? If only HDMI, then you need a HDMI/Minidisplayport-Cable. If the monitors have Displayport, then this cable works fine.