This page lists any changes in 2019.1 which might affect existing projects when you upgrade from earlier versions of Unity
Prior to 2019.1 Indirect Intensity slider only affected lightmaps when using the Progressive Lightmapper. For Enlighten, it was applied to both light probes and light maps. Now all backends apply Indirect Intensity value to both lightmaps and light probes. Upon baking the lighting again, you might notice that the probes will appear brighter if the Indirect Intensity value was modified. It is best to Clear Baked Data prior to baking lightmaps again after the upgrade.
See the UI Elements 2019.1 upgrade guide for more information.
The constructor that takes a single string is now obsolete. See the documentation for information on the supported overloads.
Projects made with Unity 2019.1 require versions macOS 10.12 or Ubuntu 16.04 or later.
The multiplayer high level API has been moved from an extension to a package. This doesn’t affect the NetworkTransport class (the low level API). All dependencies which were in the Unity engine have been moved to the package. This means the high level API is now independent except for some hooks into the profiler which couldn’t be migrated at this time.
Older Projects containing the high level API will have the package automatically added to prevent compiler errors. This does not happen for new Projects and you can add it if required from the Package Manager window. See the multiplayer high level API documentation.