There are a lot of effects in Magic that take away or add types and subtypes. The important tip to remember is that when an effect changes the type of subtype of an object, that object loses all other types and subtypes unless the effect specifically states that it keeps previous types.* For example, Adaptive Automaton will be a Construct as well as the type that was chosen as it entered the battlefield, because its static ability specifically states that it ‘is the chosen type in addition to its other types.” However the land enchanted by Spreading Seas will only have the subtype of Island as the effect from Spreading Seas does not state that this enchanted land keeps it’s other subtypes.

Another other way that a permanent can lose subtypes is if it loses the type that it’s subtype is associated with. For example, if an artifact creature with the subtype of Golem stops being a creature, it will no longer have the subtype of Golem.

*The exception to this is when an effect makes something an artifact creature, in those instances the object will retain its other types even if the effect does not specifically mention that previous types are kept.