For more information, this is the error message that is occurring:
Warning messages:
1: In cov.loglike(hess, grad) :
MLE is near a boundary or optimizer failed.
2: In ctmm.fit(ds.tel.30, GUESS, method = "pHREML") :
pREML failure: indefinite ML Hessian or divergent REML gradient.
3: In cov.loglike(DIFF$hessian, grad) :
MLE is near a boundary or optimizer failed.