My organization has seen multiple occurrences where a different user's profile picture/icon is shown besides their own. This has been seen in the OS under Start (lower left corner) as well as in Sett...
We have it for our Windows 11 24H2 as well on AVD Multi-Session.
We even hat one real issue: The elevation prompt for a specific user action, was displayed for the other user (out of context for him).
This was the same user, that got the messed image in the logout-button.