Sorry for the delayed answer.
Example A – a page with an image gallery (standard WP):
www.pfarre-mn.at/wallfahrtskirche/bilder/
Here the file name is displayed ("smart title"), not the title.
Example B – a page with a single image:
www.pfarre-mn.at/wallfahrtskirche/entstehungssage/
Here the caption is displayed, not the title.
Of course I made sure, that there actually is a title present on all images.
Settings:
• Get title from EXIF data = no
• Convert file name to title = yes
• Smart title = yes
When I change "Convert file name to title = no" then Example A displayes nothing, Example B remains unchanged.