Mitch, Thank you for your feedback. All the things you mention are already taken care of. Decent database maintenance, mega sized server, well defined DNN scheduled tasks, cleanup routines, no auto-sync, etc.
One thing different from normal is that all files are stored as “secure” files (.resources).
We have removed a lot of files and folders that the client will need no earlier than the end of this year, performance is now back to normal.
We will try to recreate the problem locally in a dev environment and do some debugging