The checks worth running before opening a ticket, in the order that finds the answer fastest.
Check that it is enabled in Admin CP, Add-ons, then check its options and its permissions. Some add-ons deliberately stay dormant until you point them at a node or a user group.
Try it on the default XenForo style first. If it behaves there, the theme is overriding something and I can usually work around it. Tell me which theme.
An upgrade overwrites the files it ships. If you had patched one by hand, that patch is gone. Tell me what the patch did, and it often becomes an option so you never have to do it again.
Rebuild the master data: Admin CP, Tools, Rebuild caches, then templates and phrases. If it persists, the server error log names the file, and that is what I need to see.
Bring three lines: your XenForo version, your PHP version, and what the server error log says. See Getting support.
Premium XenForo add-ons, built, sold and supported by the developer himself. One-time payments, 12 months of updates, forums that answer back.