# Logism shows output as X, even though the gate is connected

Below is a basic not Gate using nandgate.

Not Sure why output is X, when I change it to Output properties to three state no, I can't modify circuit.

Some times, these issues go away when I restart logisim.

some more weird issues...

My Alu output shows E

I tracked down that to below highlighted Mux gate

When I drill down to that gate it shows x on output

When I tried to modify that, it gives this popup

when I click ok and try to change input, x in output will be gone.

All my subcircuits are fine individuallly, when combining them to make ALU, these kind of weird issues popup, when drilling down, we will see results like above.

Faced same issue with adder, but restarting logisim fixed the issue.

Any ideas or pointers ...?