6 years ago, a previous employer fired me due to "retaliation" against an employee. Long story short ... the employee was on a PIP, they quit rather than be fired, they wanted to "take back" the quitting, I was ordered not to let them come back .. they filed a complaint with HR and claimed depression ... I ended up fired. Rather than fight it, I just moved on and got a new job. Is this reason for a clearance denial?
Take a read on this, it should answer your question: https://clearancejobsblog.com/why-you-should-tell-the-truth-about-why-you-left-a-job/