Engineers on my team were briefly talking about what makes a software engineer "unhireable". Not things like felonies or legal things, but more in terms of what experience they have / don't have and what they were doing before.
Is there anything in your mind that would stop you from hiring a software engineer? What are red flags to you? Again, about the skillset or experience(s), not any legal issues.
Being a senior engineer in years only, but not in skills. You become a laggard in learning new skills, and adopting good programming practices. This is the classic "1 years of experience for X years" problem. The harsh reality is that many good companies avoid these types of people. They assume that you are not proactive with your career. So it's easy to get trapped in a feedback loop where your sub-par experience can only land you offers with companies that provide more sub-par programmer experiences.