I can give you my perspective on this as a mentor, I don't know if that will help... but maybe it will!
I feel like it's my job as a mentor to make suggestions. If my student was happy with their current reviews and didn't want input on improvements, they wouldn't have joined the program. So I try to send back every review my students write, with some suggestions to consider. There have been a couple of occasions when I published "as-is" because I couldn't come up with any suggestions to improve the review.
Generally, my suggestions are about how to improve the review... meaning, the review is likely "good" as-is, but I add suggestions to make it even better. Even when I've had Advanced Reviewers as students, who regularly write "Extremely Useful" reviews, I still try to come up with suggestions to help them improve - even if it's just in small, subtle ways. Because I feel like that's why they came to me.
So from my perspective, having a review sent back to you with suggestions does not mean your review was unacceptable or bad. It simply means that you are a student, and your mentor sees it as their job to help you improve each and every review you write together.