Hi Saguaros,
Thank you for your message.
We found out what was happening: the new CSS code in 6.2.1 was restricting the total height of the hero image of the course to 200px, and thus the button was in the "overflow" part of it.
Problem solved now. In case someone else runs into the same problem, you can use this CSS code, changing the 500px to a height that works in your site:
.gru-default-layout .gru-cover{
height: 500px;
}
Best,
Roger.