Wrong Default.html layout file used
I upgraded from TYPO3 7 to 8 using my own templates/partials/layouts for fluid_styled_content. In v7 the Default.html layout file was not present so I did not have that file in my defined folder. But instead of using the default file shipped with fluid_styled content, the Default.html layout file defined for the page layout was used which should be a bug.
I defined the paths like:
for fsc: constants: styles.templates.layoutRootPath = assets/layouts/content/
for page: setup: page.10.layoutRootPath = assets/layouts/
After copying the default Default.html layout to assets/layouts/content/ everything worked again. Should I better use assets/layouts/page/ for the page layout files?
Updated by Bernhard Eckl about 4 years ago
I also had to copy Templates/Generic.html to my defined templates folder, then it worked, otherwise not. If I did not copy the Generic.html the problem remained. But if I changed Generic.html without copying and referenced to Default3.html and also renamed Default.html to Default3.html (also from the ext folder, not copied to my folder) it worked.