Hi,
exception 'Exception' with message 'failed to connect to sphinx2' in /opt/kaltura/app/infra/log/KalturaLog.php:83
Can be solved by editing /opt/kaltura/app/configurations/db.ini, setting
sphinx2.connection.dsn = "mysql:host=127.0.0.1;port=9312;"
but that is not what is causing your issue.
What do you see in the 'console' and 'network' tabs? also, look at /opt/kaltura/log/kaltura_api_v3.log checking for 'ERR:'.