I just found in a run that the calculated Hessian has a negative eigenvalue (which also result in NAs for some standard errors) and some of the gradients seems large. However, the convergence code is 0 so no error or warning is displayed. Should a warning be displayed in this case?
I tried another starting value and this problem goes away, with objective function decreases about 0.28, indicating the first run does not reach the minimum.
The code and data are in the attachment.