After enabling and configuring Segment plugin I see the following error in the browser console 

 index.esm.js:360 Failed to read configuration value at 'app.analytics.segment.writeKey' as it is not visible. See https://backstage.io/docs/conf/defining#visibility for instructions on how to make it visible.

It looks like the visibility is defined correctly https://github.com/janus-idp/backstage-plugins/blob/44cb11b80739f772f4caa4c2834287eec162b826/plugins/analytics-provider-segment/config.d.ts#L27

when I loaded the segment plugin as static it worked without any problems