1) Create new project (or download below)
2) Download Spatialization plugin
3) In audio settings enable Audio Spatialization
4) Create an audio source and set spatialize to enabled
5) Disable Audio Spatialization in audio settings
6) Press play
7) Observe the warning "Failed to initialize spatializer. No plugin has been selected. Please check that the project audio settings and the plugin importer settings have been set up correctly."

Expected a warning that better describes what is (hopefully) happening such as:
"You have audio sources with spatialize active but no spatializer plugin activated. There will be no audio spatialization. if you want audio spatialization, please check that the project audio settings and the plugin importer settings have been set up correctly."

See beta forum e-mail thread for more feedback