I've recently upgraded my Mid 2015 retina MacBook Pro's original 500 GB SSD to a 2 TB Samsung EVO 970 NVMe M.2 coupled with a recent model Sintech SSD adaptor. I am running macOS High Sierra 10.13.6. I followed the procedure outlined here.
Ever since upgrading the SSD, startup time has significantly slowed. It's now always exactly 58 seconds from chime to login screen. It used to be around 20 seconds previously.
Black Magic speed tests show good high performance. Only startup is a drag.
Is this normal? Why would it be this slow? How can I fix/improve it?