Preamble

If you want to look at merge issues (vetoes) you need to click Merge button (which is inactive). Then a popup appears:

MERGE ISSUES

There are 2 issues preventing you from merging this pull request.

...

The problem.

For many people, it is not clear that you can click an inactive button. After more than a year of using Bitbucket, they still don't know how to get problems list. Others just forget to click this button (because it is inactive). They come back next day and realize that their pull request still requires something.

Proposal 1.

Render a link "2 merge issues" right under "Merge" button. Show the popup with issues list when a user clicks this link.

Proposal 2.

Render merge issues count in red right on Merge button. Probably it will attract users' attention.