Su mejilla; es una | ola (8) (Ditto.)
¡Pobres flores de tu | alma! (8)
Probably to give the pronominal adjective greater emphasis.
Y huyó su | alma a la mansión dichosa (11)
Probably to avoid two successive stresses, though possibly there may be dieresis in mansión.
Don Félix, a buena | hora (8)
Again to avoid stress-shift under the rhythmic stress.
¡El as! ¡el as! aquí está (8)
Y si Dios aquí os envia (8)
In these two examples instead of hiatus there is synalepha with stress-shift, but we have to do with case 2 of synalepha, not case 3.