Hello,
I would start by opening your browser's dev tools and looking under both the "Console" and the "Network" tabs while making the requests in the WP I/F.
In parallel, on the Kaltura server, run kaltlog from the shell and look for any errors being outputted while making the request in WP.
kaltlog is an alias for this grep command:
tail -f /opt/kaltura/log/*.log /opt/kaltura/log/batch/*.log | grep -A 1 -B 1 --color "ERR:\|PHP\|trace\|CRIT\|[error]"
if there are errors when making the requests to the Kaltura API, they will likely show up in /opt/kaltura/log/kaltura_api_v3.log, once you've found the errors, I can guide as to how to fix them.
Also, what is your WP version?