Hi, I have seen this only when you have cloned to the new drive. Could that have happened to you? A clean install, followed by a migration should give you the recovery partition. Also, the recovery partition is invisible when booting with the alt-key. You need to boot with Cmd-R pressed. Just another guess.
Finally, this problem is also confirmed by one of the big review websites.
Unfortunately, I can't run the Phison utility on my drive, because I don't have Windows and I don't want to get it and install it just because of this. Is there a free Windows 10 anyway?
So I can only link to my own tests here.
https://forums.macrumors.com/thread...ook-pro-ssd-to-m-2-nvme.2034976/post-29941571
https://forums.macrumors.com/thread...ook-pro-ssd-to-m-2-nvme.2034976/post-29960587
My 2TB Crucial P2 in the late 2013 MBP 15", does not show a slowdown. Not after a few minutes, nor after 64GB written continously. It has not written UK CA on the label. I have had the chance to do the test on a friend's 2015 MBP 15" with his 2TB model P2 (bought 3 weeks ago on Amazon). The SSD performed close to Crucial's specs, also no slowdown, even after 3x64 GBs written.
However, I have had the opportunity to check on another 2TB Crucial P2 that has dropped write performance only after 32 GBs, sadly as low as described in the new Tom's Hardware review.