@peter Hello again.
This looks more like an issue reported by @magicalyak in the following thread:
And I don’t currently think it’s related to the 'Too many open files" thing.
But on the ‘Too many open files’ front, have a look at the following open issue where some progress has been made by the reporter, but currently on alleviating rather than fixing the issue. Interestingly their ‘open files’ look to be different from your own:
https://github.com/rockstor/rockstor-core/issues/1656
gunicorn 13354 13367 root 615u REG 0,40 592 9875127 /tmp/exports (deleted)
Have a look and see if there is anything you can contribute to that issue. Still gunicorn though.