Hi Marc,
I’ve looked at the issue, and it was a yet unknown bug. It appears that the mechanism checking if the activity feeds are active was returning false for some reason, so the search simply ignored it.
I’ve made a minor modification to the code to bypass that, namely to the wp-content\plugins\ajax-search-pro\includes\classes\search\class-asp-search-buddypress.php file. In case you update (to 4.9.5) or re-install the plugin, please make a copy of that file first and restore it once updated/reinstalled.
I’m going to fix this issue within the next upcoming update (v4.9.6) of course, I’ve noted it to be fixed.