I have some problem with a transient simulation with the AD8227 and LTSPICE..
Running the supplied test fixture is no problem, but when the common mode voltage and the Ref voltage is set to 0 the simulation stops.
As LTspice is now ANALOG this sholud be a valid question.
Try adding this statement in the schematic ".options cshunt=1e-15" to solve the convergence problem of this condition on the model.
This link will help you understand more on this convergence problems in LTspice.
By the way, the problem only appears when common-mode is set to 0 or ground and is not concerning the Ref voltage.