This has been happening for a year now.
I'm about to leave dreamhost due to this issue, but thought i'd post here before i did.
I've investigated this issue, and firmly believe there is a problem at dreamhost, with their server, or their server configuration.
But Wait! I hear you protest! Trust me, i've heard it all.
It's not my plugins.
it's not my websites.
Where's the evidence?
For a start - it's completely random. An action like updating a plugin, or saving a post, or uploading media will result in a 500 error, or a 404 time out (depending on the php version i use)
Performing the same operation again, it works. Just like that. Nothing has changed.
Unfortunately this makes managing wordpress sites frustrating and time consuming. I often have to get in to FTP and delete files, delete the wordpress maintenance files, as upgrading plugins gets stuck at a point, and the website becomes stuck in maintenance mode, or the plugin doesn't fully update.
Check your log files i hear you say. Been there, done that.
Premature end of script headers: php55.cgi
A string of text that's all over my websites error logs.
That's it. That's the common error.
It must be a permission error i hear you say.
No, it's random. Why does it not work, throw an error, and then when i hit back, do the exact same operation, it works?
Something is seriously broken. it's not my sites.
I have about 10 wordpress sites, all with different themes, different plugins, etc.
I've seen this error occur on a fresh wordpress install.
But here's how i know it's dreampress...
I've investigated two other hosts, both around the same price point as dreampress. I've migrated sites over to them. These sites are exactly the same - it's a mirror duplication.
The errors disappear on the other host, NEVER to be repeated.
Not once has the same wordpress install, moved to another host, EVER thrown an 404 or 500 error. Not once. I've been testing it for months. Same PHP version, and yes, i've tried them all on dreampress. 5/5/6/7. All throw errors. 7 seems to be the most stable, but it's not 100%. Still same problem.
Yet my sites that are still on dreampress, it's a regular occurance.
Same sites. Same plugins. Same database.
I can't help but see all these other people reporting 500 / 404 errors and think it has to do with some bug within dreamhosts systems - yet people arn't been given answers. They're being told it's their plugins. It's their websites. It's their responsibility. When really, it's dreampress.
Short of a miracle, i'll be migrating away from dreampress before my yearly renewal. 5 years of hosting, and i'm moving away. Due to this instability.
For everyone else seeing 404 / 500 errors that are random, try another host.