That error message isn’t related to your Embedded Widget - it is related to the XMR connection the player has established with the CMS for push messaging.
Essentially it means that the RSA key stored on the player does not match the RSA key stored in the CMS (the player originally sent this).
When the player receives a message, it uses its RSA key to decode it, and that fails.
It would imply that perhaps your player is not able to store the key, or create keys in general. A “rekey” action from the CMS might solve this issue - although it would be useful to find the root cause.
Can you do a rekey, restart your player and see if there any other logs mentioned?