Micah Hyde, Lang and a few others did well after they left GB, but again, those guys not being resigned wasn't really a question of talent, more a question of how much the Packers were willing to pay for the talent or to see if they got even better. This phenomenon seems to be across the board too. From UDFA's, late picks, early picks and even guys that stuck around for a long time or even given a 2nd contract. Datone Jones (4 seasons) and Nick Perry (7 seasons) are classic cases of the Packers hanging on too long and hoping for growth/consistency. Perry hasn't been resigned since the Packers released him over a year ago. Datone Jones was allowed to walk in Free Agency and after stints with 5 teams, he is still a free agent.
Then you have classic recent flops like 2nd Rd. picks Quinton Rollins and Josh Jones. Rollins hasn't played again since the Packers cut him in 2017 and Jones is hanging on to an NFL career by a thread.
All that said, I doubt this is much different than what other teams see, but if it is, the Packers might want to dig deep into player scouting and see if something needs to change.