what is the red 'x' in the schematic?

[J.Kwon]

I don't think it means cut..

[bjorn-spockeli]

If you're referring to the red x markings in our Reference Circuitry Schematics, see below, then as @RK correctly points out they mean N.C , i.e. No Connection.

[bjorn-spockeli]

The meaning is the same, i.e. it's not connected to VDD.