Page requests from non-admin users are returned without some CSS files

I’ve had this issue for at least three months.

In an incognito session:

Often when a page is request by a non-admin user, the layout is broken.
The network record shows that css files within /bb-plugin/cache were requested. The requests yield 404 errors.

I looked at the requests: the files were being requested with versioning strings. Requesting the files directly, minus the versioning strings still yielded 404’s.

Shelling into the machine and navigating to the directory, I can see that the files do not exist.

** In a non-incognito session, logged in **

I request the page. It loads normally. Layout is fine.
The CSS file has popped back into existence.

** Switch back to the incognito window **

I request the page. It loads normally. Layout is fine.

** A few hours later **

I get messages from my client. The page layout is broken. When I check, I can see that non-existent CSS files are being requested. Schrodingers CSS file has struck again.

Over the last few months I’ve found that clearing caches doesn’t work.
It’s as if the CSS file is regenerated when admin loads a page. But the it’s too snobby to stick around for mere prole users.

Clearing cache manually every day doesn’t help.
Altering the permissions in the cache directory doesn’t help.

How do make the CSS file persist?

Could be anything, whats the url for the page without the css?

URL of the site:

Note: the issue exists across the entire site.

My short-term solution was to force the regeneration of the CSS:
The CSS gets regenerated when I visit the site while logged in.
But the CSS evaporates as quickly as 20 minutes.

So I regenerated the CSS and then saved it.
I then created a custom plugin to load it.

This worked for a day.

I’ve never encountered an issue vaguely like this before.