This one is actually very simple, but I don't know how to precisely prove it:
If $(A,B,C);(C,D,E);(B,E,F);(A,D,F)$ are $4$ sets of collinear points, is it possible to prove that all these six points collinear?
This is not actually a problem, but it serves as a lemma for one of my other problems.
Here is an approximation of a counterexample: