Bottom PR of stack won't merge

[mbogdanos-plum]

🏷️ Discussion Type

Bug

Body

I’m seeing what looks like an issue with merge queue behavior for a stacked pull request.

What I’m trying to do:
Merge only the bottom-most unmerged PR in a stack

What I’ve verified:
My PR is the bottom-most unmerged PR in the stack
No rebase is required
The stack has linear history
Required checks and ruleset conditions are green
I am not trying to merge a mid-stack PR in isolation

Observed behavior:
The PR appears to get enqueued, but then nothing happens
In the browser console I see:
fetch-patch.ts:11 POST https://github.com/xxxxx/xxxx/pull/yyy/page_data/enqueue_stack 409 (Conflict)

Why this seems unexpected:
Based on the stacked PR behavior documented by GitHub, the bottom-most unmerged PR should be mergeable by itself.
PRs above it in the stack should not need to be ready if I am only merging the bottom PR.
There is no visible indication that a stack rebase is needed.

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[mbogdanos-plum]

It works today so it was probably a leftover from yesterday's outages. Closing.