Custom post type protected

hi alex,

been using your plugin for ages. always working like charm. thank you!
recentyl, we got strange problems with custom post types that shouldn’t be restricted – but are.

please check it yourself:
https://www.sonnenhaus-institut.de/solaranlagen-partner/fasa-ag
redirects any not logged in user to our registration form
https://www.sonnenhaus-institut.de/aufnahmeantrag-zum-sonnenhaus-institut.html
but the custom post for fasa is absolutely unrestricted.
i even tried setting explicitely “allowed for not logged in users”.
doesn’t help either.

all our custom post type “partner”:
https://www.sonnenhaus-institut.de/das-sonnenhaus/partner.html
most of these are – as to be accepted for any post – fully accessible
https://www.sonnenhaus-institut.de/solaranlagen-partner/1-vorsitzender-architekturbuero-dasch
https://www.sonnenhaus-institut.de/solaranlagen-partner/khb-creativ-wohnbau-gmbh
https://www.sonnenhaus-institut.de/solaranlagen-partner/wolfgang-hilz
https://www.sonnenhaus-institut.de/solaranlagen-partner/architekturbuero-dirschedl

others are inaccessible even thought 100% unrestricted:
https://www.sonnenhaus-institut.de/solaranlagen-partner/helma-eigenheimbau-ag

any idea why and how to fix this?
payment granted.
login upon request.

cheers
frank