Check your Edit > Filter settings. Make sure the Chord Symbol box is checked.

assuming you want to copy notes into measures that already have chord symbols in them, then: Edit > Edit Filter > Chords & Fretboards needs to be UN-checked before copying, NOT checked. That way the notes will be inserted but the existing chord symbols will stay put.

Sorry, I thought it was deleting the chords the OP was trying to copy. You are correct that if the chords are already in place where the OP wants them, the Chords and Fretboards option should be un-checked.