Thank you for the reply! 

I deleted the data for the specific heat (C) and the simulation results are unchanged, so this is in agreement with the statement you included from the ANSYS help. The plot below shows the results for a case with and without the C data. This is useful information but does not seem to be the problem.

The results discussed in the previous post (i.e., the plot of temperature vs time), as well as the plot above in this post, are from converged simulations. Sorry if this was not clear. I was previously having issues with convergence, but I had already enabled line search (as you suggest). I was able to get convergence with quadratic elements.

The issue that remains: The results are different when I include the additional enthalpy data point. Could you please help me understand why this is occurring?