I discovered that an .htaccess file was breaking a site of mine, throwing an "Options not allowed here" error, with Plesk which had previously worked with cPanel. I saw that this is a known issue. Disabled htaccess, index page loaded but everything else was broken due to needing mod rewrite... which works on another site. Checked Plesk help, but their suggestions don't work because we don't have access to the Apache & nginx Settings controls.
So... I just troubleshooted. Commented line by line. I discovered the offending line:
Options -Indexes
Ideally, I'd like to have them disabled, but getting the site back online was good.
Anyway, I'm posting this because I thought I'd document specifically which .htaccess directive is broken. This could help either Heliohost admins trying to resolve the .htaccess issues, or site admins trying to troubleshoot their own .htaccess issues. I would encourage other admins who figure out other troublesome directives to share them here for the same purposes.
Apologies if this thread is disruptive, duplicative, in the wrong place, etc. I searched to see if this existed already and found nothing.