On our JIRA instance we have noticed that in certain cases the ownerId of a user is their email and not the username. However, when User Avatar constructs the url for the reviewer field, it always uses the username. So for these users, the URL results in a 404.
Observed URL which results in a 404: https://tasks.opencraft.com/secure/useravatar?size=small&ownerId=<username>.
Expected URL which works: https://tasks.opencraft.com/secure/useravatar?size=small&ownerId=<user email>&avatarId=<id>
