To reproduce:
1. Open Unity 5.5, 5.6 launcher and sign in
2. Open any of these versions of Unity: 2017.1.0f1, 2017.1.1p3, 2017.2.0f1, 2017.3.0b4
3. Sign out from your account

Expected vs Actual: launcher window becomes blank

Reproducible: 2017.1.0f1, 2017.1.1p3, 2017.2.0f1, 2017.3.0b4(only sometimes)
Not reproducible: any 5.5, 5.6

Regression introduced between 2017.1.0b8- 2017.1.0f1

Workaround: sign in using Unity 5.5 or 5.6

Note:
• reproducible only on OS X 10.13 (also tested on 10.11.6, 10.12)
• sometimes it stays blank forever (longest time tested- 5mins)