This is an old issue which I thought of mentioning. Upon pressing "End Session" on the user profile being used, the End Session button shows again on the Owner lock screen. It does not go away until you press it and the screen blacks out for a second when pressing it.
Sometimes it does not have any text in the button and is a small oval button instead but it behaves the same. I doubt this is intended because once you press End Session on the Owner profile, if you open a profile again and press End Session there, that button (sometimes) does not reappear on the Owner profile.
If it makes any difference I'm using a Pixel 7 Pro and this issue has existed since February (that's when I installed GrapheneOS).
Anyone having the same issue? It's a bit annoying to keep seeing it and having to press it (OCD at play lol)