Release 1.5.0-preview.2 for Unity 2018.4 is now available as well as release 2.1.0-preview.2 for Unity 2019.x or newer. See release notes for changes.
Please continue to provide feedback specific to these release in this thread and general feedback / questions in separate threads.
IMPORTANT NOTE:
As a result of adding support for setting culling mode in the material in the Debug Settings of the material inspector, users should update the TMP Essential Resources via the “Window - TextMeshPro - Import TMP Essential Resources” menu option to import the revised shaders.