Heroku devise/facebook oauth glitch with identical source code - ruby-on-rails

Question

I try to solve problems myself, but this one has got the best of me and I'm on the verge of head-butting my desk.
Here's what I do:
I test the production oAuth, all works perfectly as it has for months
I use heroku git:clone -a myapp to get the source code locally
I make no changes whatsoever, I simply re-commit and push back up to Heroku
I test the production oAuth again, it doesn't work
I keep having to use heroku rollback, so that I can go back to the working version. I thought that since the source code is identical, maybe a gem I'm using has updated and broken something. But I checked the oAuth gems and none of them have changed for a while.
Here's my log when it doesn't work:
2015-10-25T15:20:47.802222+00:00 app[web.1]: Started GET "/humans/auth/facebook?ip=123&loc=8&mac=123&var=11" for 162.158.38.218 at 2015-10-25 15:20:47 +0000
2015-10-25T15:20:47.804207+00:00 app[web.1]: I, [2015-10-25T15:20:47.804128 #3] INFO -- omniauth: (facebook) Request phase initiated.
2015-10-25T15:20:47.871762+00:00 heroku[router]: at=info method=GET path="/humans/auth/facebook?ip=123&loc=8&mac=123&var=11" host=yourhotspot.net request_id=9804b0a9-a190-4881-a64f-ff222aa216e3 fwd="82.34.163.154,162.158.38.218" dyno=web.1 connect=0ms service=75ms status=302 bytes=1916
2015-10-25T15:20:48.181538+00:00 app[web.1]: Started GET "/humans/auth/facebook/callback?ip=123&loc=8&mac=123&var=11&code=AQCqfCPHQUM_YzgXPJSUniVKumx6ii2fsQtgEw9Bc3B9MFwNyKmnRtdqZxCRWSl1bDxdZKIAgU_M_-DQGVedt7FRYsm8DxA7gPA8bky86H-jlaCaFQa1Gc2BRLxtuzEUPKtu3UPRmKjUpXBuJI0nHOmG4IF3WWjwRk1jtfvWvgHmEH5Q-h-JjoEgiTC5uqK6XN2E48hKqxYcqBVs-pDMLMp74WRmRCXN_R_R_RuAjyyj_9-GdNHhZ6uajuri_41AN5V8W9UqWPmtPHznL7ztNLzS9dDj7S9e25bINXUMneHVVNHwGpp5PWZULsN_hwJueUU4SFZlNgzrnupacHAXF9kU&state=1e8f5be4b10b96baedd6aab3cd2eb125b150e100c5a2c7bb" for 162.158.38.218 at 2015-10-25 15:20:48 +0000
2015-10-25T15:20:48.183305+00:00 app[web.1]: I, [2015-10-25T15:20:48.183218 #3] INFO -- omniauth: (facebook) Callback phase initiated.
2015-10-25T15:20:48.733053+00:00 app[web.1]: {"error":{"message":"Error validating verification code. Please make sure your redirect_uri is identical to the one you used in the OAuth dialog request","type":"OAuthException","code":100,"fbtrace_id":"B8bmqcG7i6M"}}
2015-10-25T15:20:48.733049+00:00 app[web.1]: E, [2015-10-25T15:20:48.732948 #3] ERROR -- omniauth: (facebook) Authentication failure! invalid_credentials: OAuth2::Error, :
2015-10-25T15:20:48.735557+00:00 app[web.1]: Parameters: {"ip"=>"123", "loc"=>"8", "mac"=>"123", "var"=>"11", "code"=>"AQCqfCPHQUM_YzgXPJSUniVKumx6ii2fsQtgEw9Bc3B9MFwNyKmnRtdqZxCRWSl1bDxdZKIAgU_M_-DQGVedt7FRYsm8DxA7gPA8bky86H-jlaCaFQa1Gc2BRLxtuzEUPKtu3UPRmKjUpXBuJI0nHOmG4IF3WWjwRk1jtfvWvgHmEH5Q-h-JjoEgiTC5uqK6XN2E48hKqxYcqBVs-pDMLMp74WRmRCXN_R_R_RuAjyyj_9-GdNHhZ6uajuri_41AN5V8W9UqWPmtPHznL7ztNLzS9dDj7S9e25bINXUMneHVVNHwGpp5PWZULsN_hwJueUU4SFZlNgzrnupacHAXF9kU", "state"=>"1e8f5be4b10b96baedd6aab3cd2eb125b150e100c5a2c7bb"}
2015-10-25T15:20:48.735493+00:00 app[web.1]: Processing by Humans::OmniauthCallbacksController#failure as HTML
And when it does:
2015-10-25T15:56:56.726873+00:00 heroku[router]: at=info method=GET path="/humans/auth/facebook?ip=123&loc=8&mac=123&var=11" host=yourhotspot.net request_id=1c01da5f-1bea-4dbb-9a1b-a80dcc442539 fwd="82.34.163.154,162.158.38.211" dyno=web.1 connect=1ms service=18ms status=302 bytes=1828
2015-10-25T15:56:56.714754+00:00 app[web.1]: I, [2015-10-25T15:56:56.714674 #3] INFO -- omniauth: (facebook) Request phase initiated.
2015-10-25T15:56:56.920771+00:00 app[web.1]: I, [2015-10-25T15:56:56.920692 #3] INFO -- omniauth: (facebook) Callback phase initiated.
2015-10-25T15:56:56.712897+00:00 app[web.1]: Started GET "/humans/auth/facebook?ip=123&loc=8&mac=123&var=11" for 162.158.38.211 at 2015-10-25 15:56:56 +0000
2015-10-25T15:56:56.919315+00:00 app[web.1]: Started GET "/humans/auth/facebook/callback?code=AQC7jHL3hk8TSP5F9lsDjzkyXlAIbk-Kf3027g3bU-9x0etBoOxUvHd6ofEIZjEolh-UajkUCS4WZ3z40q7tgrIYi8ZIy6fuhjRJwyqLhXBPfOnmL1LqCDlPFVIdizrHPUomZ5WZ-VLmFc7A1UsEUVpyW907LgoaL8S90Gukh9oGvykIcpc1tmHqpc-WaayJNCkTUPxaRtlEmuD5FTVUDoRAzFnVDYCURhNAZMs9eTk-O40_leapHbTX0Uz6sFC6RHn-qgien_diOJst2DlRvtKWCcfxXuoBZPFPa5BtRYg2_eP4K8zUxRtDeazwYsxJt7o1i9V93np56EABMMrfBmIK&state=952e4d3cbe773056b12f56d76b0a54c5ea841f51e61d5041" for 162.158.38.211 at 2015-10-25 15:56:56 +0000
2015-10-25T15:56:57.897756+00:00 app[web.1]: Processing by Humans::OmniauthCallbacksController#facebook as HTML
I just cannot wrap my head around what's going on here. The fact that my code, environments, config vars and app settings are identical is hurting my head.
If anyone can shed some light on what might be going wrong, I'd be very appreciative.
EDIT: (Commands used)
heroku git:clone -a myapp (At this point of cloning, I had already rolled back to v410, so this clone should be of that working copy)
(cd into new app directory, make a line
change so that I can re-commit)
git add .
git commit . -m "msg"
git push heroku master
(realise it's not working as expected)
heroku
rollback v410
Command logs gave no errors and the commands worked as expected. Yet something is changing oauth.

Answer 1

What definitely could change on deployment is a physical server ('dyno'). I would check following things: 1) does your app cache any authentication tokens issued by facebook, e.g. in configuration? 2) how possible is that such tokens are bound to the server's IP address?