Why does my D Flip Flop Circuit have an X output?
Seems to me like your flip flops need to have a reset value. 

When power is applied to a DFF at "time=0", the output state is X, or unknown. A reset is needed to bring the DFF to a known state.

In your case, check out the FF DB. It's input is:

(DB &amp;&amp; !DA) || (Sensor &amp;&amp; !DB &amp;&amp; DA). 


When I substitute your time zero values into this I get:

= (X &amp;&amp; !X) || (0 &amp;&amp; X &amp;&amp; X)
= ( X || 0 )
= X


So until something happens that actually forces the inputs to a non-X value, the circuit will have an X state forever. A 'reset' would typically be used to clear the Xs.