When you project an object into a sketch you get Purple lines to work with.
If you delete - or radically alter - the geometry of that original object those lines remain but turn YELLOW.
Sometimes deleting all those yellow lines in a sketch can really be a pain:
1) usually they're mixed up with your sketch lines and with valid purple project lines that you want to keep;
2) F360 seems to be fussy about how you select a line for deletion, eg you can't select an accessible endpoint but must select the body of the line. Sometimes that's awkward!
I think it would be great to have a shortcut / menu option to simply "delete all expired / invalid / yellow projection lines from this sketch". Then one can get on with the proper job of creation.
Below an example image showing yellow lines that must be deleted from a sketch.