Artificial muscles, designed to replicate the movements of natural biological muscles, hold significant promise in the fields of robotics and prosthetics. Recent advancements have led to the development of fiber-reinforced actuators, drawing inspiration from biological tissues. Dielectric elastomer actuators (DEAs) are a type of electroactive artificial muscle. It is possible to enhance the uni-axial deformation of DEAs by constraining and applying pre-stretch on the actuator membrane. This can be achieved through uni-directional fibers bonded to the DEA that lead to transversely isotropic properties. However, combining membrane pre-stretch and fiber reinforcement may lead to instabilities such as fiber buckling due to the compressive load of the pre-stretched membrane or due to wrinkling during actuation. Understanding these instabilities is crucial as they can significantly impact the performance. A novel model taking into consideration these instabilities is established and experimentally validated. By calculating the force in the fiber direction, the buckling profile such as the wavelength and amplitude can be predicted. The validation of the model presented along with an extensive experimental investigation allow for a comprehensive analysis to explore the impact of fiber buckling on the performance and the force of uni-axial DEAs.