How can a store to a variable be reordered after a load of that variable, given single-threaded serialization guarantee?

Question

Lets have a simple code snippet

   import java.invoke.VarHandle.fullFence;
   ...
   int x = 42;
   int y = 42;
   ...
   x = 1;
   fullFence();
   x = 0;
   y = x;
   fullFence();

   //another thread
   if (y == 1)
      System.err.println("wtf?");

There is another thread which reads x and y - I am trying to reason what kind of guarantees it gets from this code, before adding fences itself.

Considering that the thread executing that snippet must see y==0 after the second fence, can load(x) and store(x, 0) from between the fences be actually reordered with each other? If so, then why?