Not sure why it's not working. Just did a quick test here using 1.4.5, dropped in a couple of clips into a 2:1 timeline, then exported to Facebook with default settings and VR set to 360 Mono.
I have seen Facebook be a little flaky about recognizing the metadata (not sure why), so it might be worth doing another try. When I exported it was at 1440p (2880 x 1440), 30 fps, Standard Quality (24 mbps), 44.1KHz audio, mpeg4 format, and 360 Mono.
Also, try uploading to Youtube and see if that works any differently.
If it still doesn't work, contact us at firstname.lastname@example.org
and we'll have you send your project so we can see if we can reproduce with it.