If I set the user notification level on user page it will revert to the default (which were you previously set up in settings to the user i think) level after reload the page.
On settings page /preferences/users it works fine.
A recent commit caused an object { level: "muted" } to be passed to the server instead of a string value. I have a PR that fixes that issue, as well as the server throwing an error when the level param is not valid. For the review - it also fixes a JS deprecation due to overriding a computed property (by adding a set)