I just encountered this bug today while setting up SSL certificates for electrumx servers.
The problem was very simple and stupid. For some reason the live and archive folders in the /etc/letsencrypt tree had no execute permissions.
ElectrumX was unable to read its certificates, of course. This was on both Arch linux and Ubuntu 16.04.
For some reason it is not well known by many people at all that the execute permissions on directories influence the cd command. If you have a user level permission file inside another folder that lacks the X permission on the enclosing folder, you cannot access the file even though the file itself has read/write/execute permissions granted relevant to the user trying to access it.
/
|
folder root rwx------
| |
| file user rwxrwxrwx
If this is what the permissions look like, even though the file is permissioned to allow unlimited access, only the user who owns the folder can enter the directory, or read the file.