The cross means that there is only one connection to that net. When you click on a net in the design manager it shows the pins that are connected to it at the bottom of the panel. Click on a pin to highlight where it is.

ok  that is what i do but 3V3 is a power supply  so a lot of pins are connected to and i do notsee  ratlines on it. but : i stopped  my work to wait your answer and when i restart after time  and i open again the layout the cross  disappear on 3V3 without i did nothing !!! can you understand why ? 2  how do i force to check the net again after correction or it is automatic ? thank you