๐ฌ FAQ๐
Mergify is unable to merge my pull request due to my branch protection settings๐
This happens usually if you limit the people that have the authorization to
merge pull requests. To make it works with Mergify you must add Mergify
to the
branch protection settings in the "Restrict who can push to matching branches" list.

Why did Mergify seem to have merged my pull request whereas all conditions were not true?๐
The GitHub user interface might be misleading you in thinking that your pull request has been merged by Mergify, while it wasn't.
If your pull request A has all its commits contained in another pull request B, and if B is merged by Mergify, then A will appeared to have been merged by Mergify too. GitHub detects that A's commits are a subset of B's commits and therefore decides to automatically marks pull request A as merged.
Be sure that Mergify did nothing on the pull request A if it told you so in the Checks tab. Don't be fooled by GitHub UI.