Some users have experienced sign in issues after an ssd upgrade. If this occurs, simply reset the console (keep games and apps if need be.) and that should resolve the issue.
Those who have their Xbox set to "energy saving" mode for startup may experience a 20-30 second black screen before boot. Changing this setting to "instant on" resolves this issue.
Now enjoy 20x faster r/w speeds and loading times a fraction that of a standard HDD.