Seems like that should be for something else, as we only have one branch in this repo, master. So it's not a case of not looking at other branches for the merge commit.
What I've suddenly noticed, when looking for the commit in gitiles, I can see it in the history, but gitiles cannot display the merge commit, but if I clone the repository it's possible to look at the merge commit, and if I select an earlier merge commit that was created by Gerrit (need to go a few 3) it displays fine. But this commit along with another 5 merge commits created by Gerrit submitting commits do not display when trying to view with gitiles.
Does this provide a further clue on what to look at?
Is there a cache/index issue here for some of these merge commits? or something wrong with the repository at that point that causes issues with jgit?
Darragh