since bootstrap 4 the scssphp compiler breaks on some parts if the bootstrap is used unmodified. In moodle 3.5 two files from bootstrap has been modified. The modification is just a comment mark on the problematic lines.
Because there isn't a note anywhere it took me hours to find the reason why I didn't get carousel which run correctly.
To solve this I readded the removed parts in the css representation. With that the compiler did the job right.
If someone is intrested in solving this issue please have a look here: