I'm using api to determine the tip revision to decide whether a repository mirror is in synch with the source repository. This has worked well for quite a long time, but in the past few months I've found some repositories reporting the wrong mercurial node for Tip. The tip revision seems to be going stale (i.e. after several weeks I notice that tip is reporting a very old revision). If you use the scm manager repository interface you'll see newer revisions present on the repo. Also cloning these repositories shows tip to be a much newer revision.
Restarting scmmanager process fixes the problem temporaraily.