Do you think that the problem is with the fact that you're using a Samsung EVO Select made by Samsung for Amazon, as opposed to using an EVO Plus original - tests show that the Samsung made for Amazon Select green version is both quicker and more expensive.
Or do you think the problem lies with using the larger capacity of 512 GB vs only 256 GB?
....
Posting another answer to your question to provide some closure.
After much testing I determined that the card in question was performing well below spec. While it's rated at 90 MB/s write speed in actual use it was only achieving 1.8 MB/s. Little doubt in my mind that's the cause of the problem. See test results below.
I have started the warranty exchange process with Amazon.
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Samsung 512GB Test 1
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CrystalDiskMark 3.0.3 x64 (C) 2007-2013 hiyohiyo
Crystal Dew World :
http://crystalmark.info/
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* MB/s = 1,000,000 byte/s [SATA/300 = 300,000,000 byte/s]
Sequential Read : 85.084 MB/s
Sequential Write :
1.862 MB/s
Random Read 512KB : 76.900 MB/s
Random Write 512KB :
1.864 MB/s
Random Read 4KB (QD=1) : 10.394 MB/s [ 2537.6 IOPS]
Random Write 4KB (QD=1) : 0.961 MB/s [ 234.6 IOPS]
Random Read 4KB (QD=32) : 10.901 MB/s [ 2661.4 IOPS]
Random Write 4KB (QD=32) : 1.011 MB/s [ 246.9 IOPS
================================================================
Samsung 512GB Test 2
Sequential Read : 87.236 MB/s
Sequential Write :
1.870 MB/s
Random Read 512KB : 78.045 MB/s
Random Write 512KB :
1.856 MB/s
Random Read 4KB (QD=1) : 10.208 MB/s [ 2492.1 IOPS]
Random Write 4KB (QD=1) : 0.955 MB/s [ 233.0 IOPS]
Random Read 4KB (QD=32) : 11.012 MB/s [ 2688.4 IOPS]
Random Write 4KB (QD=32) : 0.960 MB/s [ 234.4 IOPS]
====================================================================
Transcend-1 64GB
Sequential Read : 85.724 MB/s
Sequential Write :
23.152 MB/s
Random Read 512KB : 75.010 MB/s
Random Write 512KB :
17.139 MB/s
Random Read 4KB (QD=1) : 3.759 MB/s [ 917.7 IOPS]
Random Write 4KB (QD=1) : 1.103 MB/s [ 269.2 IOPS]
Random Read 4KB (QD=32) : 5.105 MB/s [ 1246.4 IOPS]
Random Write 4KB (QD=32) : 1.164 MB/s [ 284.2 IOPS]