Bug when using shortcode from another plugin

I’m using the custom tab plugin and it’s very easy to use but I wanted to add a custom tab for a mp3 player that plays sample mp3s. Therefore I used the mp3 jplayer plugin.

Within the custom tab I use the shortcode:
[mp3-jplayer tracks="FEED:/htdocs_folder/folder_with_mp3s_in_the_wp_main_directory"]

It only loads some buttons of the player but nothing is playing. But if I use this shortcode in the description tab AND the custom tab it works.

What could cause that and how to debug? Is the path to the mp3 folder wrong because the custom tab plugin is in another directory? Or is it something with the order of the scripts?

Regards

https://www.ads-software.com/plugins/woocommerce-custom-tabs/