As a user, I don't see chapters for all podcasts

Describe the bug

After the release of the chapter display feature, as a user I don't see the chapters on all podcast's episodes.

Steps to reproduce

For published podcasts :

1. Go to https://podcast.projets-libres.org/@projetslibres/episodes/castopod-est-son-propre-reseau-social-episode-2-y-doghri-et-b-bellamy-ad-aures/chapters , a chapter tab is displayed, but no chapters are available
2. In a podcast client app (for example AntennaPod), chapters are available for this podcast.

When previewing a non published podcast : Castopod displays the chapter tab, but is unable to list chapters.

Expected behavior

All chapters are displayed for published and non published podcasts.

Actual behavior

Chapters are available for some episodes but no all episodes. Chapters are not available for podcasts in preview mode.

Relevant logs and/or screenshots

Context

• Castopod: castpod.com, version 1.10.3

Possible fixes

[If you can, link to the line of code that might be responsible for the problem]