I found a code that caused this problem.
Our servers employ the Kaltrua CE 14.18.0, and the version of KMCng is 5.7.1.
The “/opt/kaltura/apps/kmcng/v5.7.1/main.56e763caa0a388ded4f6.js” includes the following code:
This code generates URLs that begin with “http” regardless of whether the Kaltura server is secure or non-secure.
In order to get URLs starting with “https”, please replace “http” with “https”.
We should modify this code to add “http” or “https” depending on the CDN server’s protocol.
But, I don’t know how to fix it.