Probably something on your end, it is using a normal letsencrypt cert
/ # stat /dev/null
File: /dev/null
Size: 0 Blocks: 0 IO Block: 4096 character special file
...
/ # sed -i 's/foo/bar/' /dev/null
/ # stat /dev/null
File: /dev/null
Size: 0 Blocks: 0 IO Block: 4096 regular empty file
...