We cannot confirm the exact issue but in your current code snippet we found the following errors
$appContent is not defined anywhere in the hook. qloAngular_calendar.tpl template is called multiple times which is not required, also the variable $calendarContent is not used anywhere. // The following code is not required as $this->display() function fetches and returns the passed template by default. $calendarContent = $this->context->smarty->fetch($this->local_path . 'views/templates/hook/qloAngular_calendar.tpl');Please enable debug mode which will help in further debugging the issue
https://devdocs.qloapps.com/introduction/configuration.html#debug-mode-error-reporting