Co-injection marker without transgene

Hi everyone, I microinjected some worms with the coding sequence of an exogenous protein (polymerase) to express along with a fluorescent co-injection marker (myo-2::GFP). The F2s show the coinjection marker but PCR for the transgene did not reveal any DNA. How is this possible? Could the worms be losing the transgene somehow but not the co-injection marker? Thank you!