Error: Call to a member function page() on null

Podlove 2.9.0
Wordpress: 5.2.2

As soon as I try to change the new iTunes categories an error pops up and I got an automated mail from my website:

Ein Fehler vom Typ E_ERROR wurde in der Zeile 47 der Datei /usr/www/users/useful/wp-content/plugins/podlove-podcasting-plugin-for-wordpress/lib/settings/expert/tabs.php verursacht. Fehlermeldung: Uncaught Error: Call to a member function page() on null in /usr/www/users/useful/wp-content/plugins/podlove-podcasting-plugin-for-wordpress/lib/settings/expert/tabs.php:47
Stack trace:
#0 /usr/www/users/useful/wp-content/plugins/podlove-podcasting-plugin-for-wordpress/lib/settings/podcast.php(59): Podlove\Settings\Expert\Tabs->getCurrentTabPage()
#1 /usr/www/users/useful/wp-includes/class-wp-hook.php(286): Podlove\Settings\Podcast->page('')
#2 /usr/www/users/useful/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters('', Array)
#3 /usr/www/users/useful/wp-includes/plugin.php(465): WP_Hook->do_action(Array)
#4 /usr/www/users/useful/wp-admin/admin.php(253): do_action('podlove_page_po...')
#5 {main}
thrown

edit:

the error is just minor!
grafik

It refers to this message. The link in this message leads to:
https://usefulvid.com/wp-admin/admin.php?page=podlove_settings_podcast_handle&podlove_tab=directory

but if I click on the tab manually if have this link:
https://usefulvid.com/wp-admin/admin.php?page=podlove_settings_podcast_handle&podlove_tab=verzeichnis

and this works fine