I have solved this.
In order to make the scrolltotop button work correctly on podcast pages (hide at top and show after scrolling) I had to remove the custom css we added in the child theme:
.single-podcast .scrollToTop {
display:block !important;
/*z-index: 9999999 !important;*/
}
…and then remove this code from theme.min.css:
.single-podcast .scrollToTop{display:none !important}

Hi Azam.
With the new version of the theme this problem has returned.
The back to top button shows on pages but not on podcast posts.
Whatever you changed previously has obviously been overwritten by the new version of the theme.
Please advise.