When dealing with slots, the behavior is a bit complex (and you might argue confusing!). The trickiness comes from the fact that the deployment history moves with the content of the site when you perform swaps.
I'll illustrate by example:
- You start with a production slot (i.e. the main app), and a staging slot. No deployments have happened yet.
- Deployment #1 happens to the Staging slot
- You swap to production
- At this point, you will see no history in the Staging slot because the history was swapped to the Production slot.
- Now you deploy #2 to the Staging slot, and you swap Production.
- The history on the Staging slot now has #1, as it got swapped back in there.
- Deploy #3 and swap
- The history on the Staging slot now has #2.
- Next time you swap again, the Staging slot history has #1 and #3
So you get the idea: each slot will contain alternating history items. #1, #3, #5, etc in one slot, and #2, #4, #6, etc in the other.
To make this a bit more subtle, while both slot contain history items, the Portal only shows history for slots that are enabled for deployment. So while your Production slot contains history items, the Portal does not show them (this does need to be addressed).
As a workaround, you can go to https://{yoursite}.scm.azurewebsites.net/ and click on Deployments to get the deployment list in the Production slot. This is a REST API, and not a fancy UI.
Hopefully this helps clarify this admittedly confusing behavior :)