PRs left uncombined despite no merge conflicts

Occasionally (and lately, near consistently), I am seeing combine-prs claiming that some PRs were left out due to merge conflicts. Investigating the relevant PRs, I see no reason they would be in conflict. Out of curiosity, I deleted the PR and branch and re-ran the combine-prs action, and it results in a clean combine-prs PR, including the previously-excluded PRs.

I have not verified, but this makes me wonder if it's a timing-related issue between when e.g. dependabot creates PRs and a subsequent combine-prs scheduled run attempts to combine them.