I had this issue from the beginning. I made multiple fresh installs and nothing new. I've checked the ssl_error_log and I was getting this:
PHP Fatal error: Uncaught --> Smarty: Invalid compiled template for 'common/list.tpl' <-- \n thrown in /usr/share/php/Smarty/sysplugins/smarty_internal_templatebase.php on line 182
So, the _list.tpl was the reason for triggering the HTTP Error 500.
Whoever has this problem with _list.tpl, here's the weird fix:
I have just renamed _list.tpl to list.tpl and it started to work like a charm.
If you decide to rename, you should make changes in the following file:
/libs/paloSantoGrid.class.php # on line 245 you'll see this: $this->tplFile = "common/list.tpl";
So, just take off the underscore from "_list.tpl" to "list.tpl"
@fabarcap & @cmfs you both seem to have a problem with permissions on /cache/ folder. Give permission to 644 for files and 755 to the cache directory.
run:
find /var/www/html/cache -type d -exec chmod 755 -- {} +
find /var/www/html/cache -type f -exec chmod 644 -- {} +
Hope this helps.