I’m not seeing anything jump out at me from the app.yml.
_Off Topic: when pasting in code, it is helpful to surround it with 3 back ticks. Reference: http://commonmark.org/help/tutorial/07-code.html_
The only thing I haven’t seen before is SEGMENT_IO_KEY. I’m assuming that’s related to this plugin? GitHub - kylewelsby/discourse-segment-io-plugin: Emits user events to segment.io · GitHub Does the error still occur when the plugin is removed from your app.yml?