In this case it seems like the issue was PHP version as customer has old Magento.
It seems like a update from your servers caused the PHP version change in WHM.
Customer was using native, but it was changed to use ea-php and not alt-php, even though logs show something else:
[Tue Apr 09 02:50:23 2019] sulsphp: uid
557/username); gid
557/username); with suexec mode; cmd
/opt/cpanel/ea-php70/root/usr/bin/lsphp)
[Tue Apr 09 02:51:09 2019] sulsphp: uid
557/username); gid
557/username); with suexec mode; cmd
/opt/cloudlinux/alt-php53/root/usr/bin/lsphp)
Not sure why you show incorrect or like that in the logs though.
Customer is now using Alt-PHP 5.6, but showing this in sulsphp_log:
[Mon Apr 15 12:36:06 2019] sulsphp: uid
557/username); gid
557/username); with suexec mode; cmd
/opt/cpanel/ea-php70/root/usr/bin/lsphp)
