missing necessary objects on push

Pulled in new upstream changes, rebased my local master on upstream/master, want to push to origin (my fork):

*   de6db44 - (HEAD -> master, upstream/master) Merge pull request #73
|\
| * 6adff2b
| * cdeca2c
|/
*   45dbc89 - Merge pull request #72
|\
| * 210037c
|/
*   552dcb8 - (origin/master, origin/HEAD) Merge pull request #71

try pushing to Github enterprise instance:

$ git push origin master
Total 0 (delta 0), reused 0 (delta 0)
To github.vpn:org/repo.git
 ! [remote rejected] master -> master (missing necessary objects)
error: failed to push some refs to 'github.vpn:org/repo.git'

but!

pushing the non-merge commit related to #72 works:

$ git push origin 210037c:master
Total 0 (delta 0), reused 0 (delta 0)
To github.vpn:org/repo.git
   552dcb8..210037c  210037c -> master

pushing the merge commit related to #72 does not:

$ git push origin 45dbc89:master
Total 0 (delta 0), reused 0 (delta 0)
To github.vpn:org/repo.git
 ! [remote rejected] 45dbc89 -> master (missing necessary objects)
error: failed to push some refs to 'github.vpn:org/repo.git'