All puppies go through stages of development. Two of them are often referred to as the fear period or stage. The author explains each stage and ways to help a pup mature into a confident, happy, socialized dog.
For most dogs animal health pros see, stage 1 has already passed during weeks three through twelve. Stage two generally arrives at about four to six months and can last up to age 14 months, depending on the dog. Stage two pups are reaching adolescence and once confident pups can suddenly get cautious, worried or approach things differently than they did when they were younger.
Source: German Shepard Shop. Link.
While puppies are going through a fear stage, it’s important to stay patient and not force the dog to approach or accept something they find worrisome.”