We have experienced that the web_ui part of the ticket crashes with No such changeset error and renders nothing else if someone has chosen to rebase or the like (re-commit) on a repository.
We made a small fix for our own installation by adding a try except handler in the expand_macro function in the web_ui.py module.
changeset = repos.get_changeset(rev)
message = changeset.message
rev = changeset.rev
return tag.div(tag.p(_("(No such changeset)"), class_='hint'),
We hope that this (or a similar fix) will find it's way into the code :)