LP 3.0.7 shows no lessons with the-core theme

I have the-core theme running on my page and installed LearnPress 3.0.7. All lesson texts were gone – you could just see the comments section. I reverted to LearnPress 2 – works fine.
On a different installation I removed the the-core theme and LearnPress 3 works (I did not do a deep testing) – so I guess there is something with LP 3 and the-core that’s not working.
Any ideas?
Thanks Edgar

The page I need help with: [log in to see the link]