I had a 12Tb unit and recently bought a 16Tb unit. Whenever I have one of the 2 installed/connected I cannot see or connect the other. What do I need to do, please?
Make sure each unit has a unique name. Use the My Cloud Dashboard to change the name of the second (or additional) unit.
Also, you may want to see the dedicated EX2 subforum since this subforum (My Cloud) typically discusses the single bay My Cloud units.