He’ll probably need another year in low A.
Not sure that's really a problem. He'll be 20 all of next season, which would put him at 21 in high-A, a fairly normal prospect track. HS draftees are basically doing low minors instead of college.
If he were a college draftee at his slot and struggling in low-A now, I'd absolutely be worried, but that's just not what's going on.
For example, Hassell is 21 right now (22 in August) and not tearing up AA, so he's looking like more AA next year, which also doesn't take him off the prospect radar. Yeah, they have to do it eventually, but some struggles in the low minors are very common for HS guys.