I uninstalled Themehouse, and re-installed the add-on. The error appears again.
#0 [internal function]: XF\Template\Templater->handleTemplateError(2, '[E_WARNING] uso...', '/var/www/vhosts...', 329, Array)
#1 src/addons/EWR/Discord/Repository/Discord.php(329): usort(false, Object(Closure))
#2...