In Unity 5.4 it's possible to set the rendering path via Player Settings, however in 5.5 this has been replaced with the Tier settings in the Graphics Settings menu. Everything in this rollout is simply set to a default value of using Forward, and doesn't respect whatever the user's setting was in earlier versions (resulting in a loss of data, however minor).

Reproduction Steps:
1. Take a Unity project prior to 5.5
2. Set the rendering path to Deferred in Edit > Project Settings > Player > Other Settings
3. Open the project in 5.5 and navigate to Edit > Project Settings > Graphics
4. Observe that the rendering path is now Forward

Expected Result:
User settings from earlier versions of Unity should not be lost due to upgrading, or if they are this should be better communicated to the user so they can take action rather than seeing potential graphical issues without understanding where they have come from.