What's the next step if found fit for duty during a chapter 5-17 separation?

I can help answer your question, but you have to iterate a couple of things. You state that you are going through a Chapter 5-17, and you also highlight that a Separation Board is reviewing your case. Is your Chapter --- command directed? You can inbox me to keep your private medical information off the public site.

c. Chapter 5-17 (Other Designated Physical or Mental Conditions). This Chapter is very
similar to Chapter 5-13, except that it covers conditions that fail to rise to what the doctors call a
“disorder.” These are conditions such as chronic airsickness or seasickness, dyslexia, sleepwalking, claustrophobia or “other disorders manifesting disturbances or perception, thinking, emotional control or behavior sufficiently severe that the Soldier’s ability to effectively perform military duties is significantly impaired.” The key factor is that the condition must significantly impair a Soldier’s ability to perform his/her assigned military tasks.

These are subjective things, observations and opinions.. ,,as such providing the Admin Sep board submit matters for the separation authority to consider before the separation authority makes a final decision regarding separation is likely to not prevail, as it would be difficult to provide tangible facts in most cases to counter another's thoughts, feelings, opinions and personal observations.