Old build is displayed in Branches tab

TeamCity 2019.1, Classic UI.

Build configuration has a Mercurial VCS root with two branches, "default" and "ReleaseCandidate". The Branches tab of this build configuration shows these two active branches. A few months ago I notices that "default" branch is displaying an old build with old number although more recent builds are available in Overview and History tabs.

We have many other build configurations with similar branch specifications, but the problem described above is observed only on one of them.

Upd: every next build running that "default" branch has an exclamation popup "This build is outdated (more recent build [that old number] is already finished" during build process. But after the process complete this popup disappears.