For same session UserID is send as 'anonymous' and ID for signed in user.

To repro:
0. The issue is floating, so you'll need to try for several times.
1. Run Unity as signed in User.
2. Open project.
2.1 Note UserID in SessionInfo event.
2.2 Note UserID in EditorStartups event.
2.3 Note UserID in ProjectSnapshot event.
3. Open another project.
3.1 Repeat 2.1-2.3
4. Close Unity.
4.1 Note UserID in SessionInfo event.

Actual result: In some of this events UserID would be set to anonymous, for other - as ID. All other data is correct.
Expected result: User ID is set always as ID, if the user is signed into Unity.

Appears from 5.5, did not find it in 5.4.0b12.