Yes, there are recently not visible if you choose directly SIN-sth e.g. PEK-SIN, SIN-AKL but if I choose WAW-SYD, I can find C WAW-CPH-SIN-SYD. Few weeks ago, there was (I understand mistake) possiblity to book F (A380) on SQ online and then suddenly they hide F but looks like also C.