Hi! I've got a mid 2012 13" Macbook Pro. I've bought a Samsung 860 Evo 600gb. Initially I just installed the SSD in the HDD bay as you'd expect and attempted a clean install of High Sierra from USB. The install was excruciatingly slow taking 9 hours. I next attempted to connect the SSD by the USB adapter. The OS installed quickly. I put the SSD back into the internal bay and everything slowed right down; booting took an eternity then clicking anything when it'd booted caused it to lag. I did think that the SATA cable could have somehow damaged itself in the process but the original drive, back in the Macbook performs normally. Any solution for this problem?