I know I had a couple issues to work through to get SSL working with Metabase, are you running the .jar version?
For the .jar version on linux I created a small bash script that before calling metabase.jar set some of the JETTY ENV variables. This can be done other ways, this was just easiest because I had to pass some flags to the metabase,jar anyways.
As well make sure you can see your cert in the keystore after importing.
Would you mind sharing an example of what your Metabase embed code looks like and where it is applied when embedding into a WordPress page? The jwt related code in particular, does that go into a existing php file? References to any resources on the topic would also be appreciated. Thanks!