Troubleshoot asset file issues

What does this MR do?

It also happens with development environments, but shouldn't happen with K8S or docker installs because these run in such a way that the Puma processes and asset files "on disk" should always be a complete and matching set.

From research previously (see related issue) there's four ways this issue can arise, and they're documented in order of likelyhood - stale Puma processes, duplicate sprockets files, a broken package install, or site reconfiguration of NGINX.

Related issues

#344152 (closed)

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