Oops, sorry, indeed, I miss that info from the first post.
I’m afraid it’s a “feature” from Exchange. The server calendar visibilities is exported to the device. One should modify the source of the EAS plugin to apply the same solution than the one applied for colours : store last seen server visibility and apply it only if it changes, otherwise keep the device choice. I’ve done it for CalDAV colour issues and @flypig did the same for Google accounts. Sadly the EAS plugin is closed source and I cannot do anything for it.
See also :