Thanks for your quick response.
I have a report of it slowing down Woo checkout. There is a support thread that documented that I’m sure I can find when I’m back on desktop.
But mostly it kills admin load time when saving posts and pages. It seems to come and go from site to site.
Might be worth noting my var/www isn’t owned by www-data, just the group. We’re a bit more locked down for SFTP users and use ssh2 as the FS_METHOD in our config. Not sure if it’s relevant.