Check your handbook. It has extremely detailed examples about what can lead to probation.
Off the top of my head it's either fund of knowledge (low ITEs), behavioral issues (too many people complain about you), or psychosocial issues (alcohol, drug use).
I read the handbook. It's still vague. It says:
Academics:
1) Issues involving knowledge or skills
2) Job performance or scholarship
3) Minor professionalism concerns.
B. Misconduct
1) Unethical conduct, such as dishonesty or falsification of records
2) Significant professionalism concerns
3) Illegal conduct (regardless of criminal charges or criminal conviction)
4) Sexual misconduct or sexual harassment
5) Workplace violence
6) Tardiness, absenteeism, or job abandonment
7) Boundary violations with patients
8) Failure to meet conditions of employment
9) Violation of (hospital) or other applicable policies or procedures.
I guess I need concrete examples of what it means to have deficient skills, poor job performance, etc and how pervasive it needs to be.