Even if honesty is always good in the face of a well-meaning, non-prejudiced person that knows and has the confidence to know that you mean well and are not prejudiced too…
You don’t have to worry about honesty. It’s not about honesty. It’s about usefulness.
Clearly, the current situation is harmful to you, and the instructor causes that, probably both without intention or being aware of it. It may be the deciding factor to the avalanche that decides your future, after all.
So how about you not getting hurt either?
You can ask yourself: What is the most useful? To the instructor. To you.
Both directly, in terms of plain information given, as well as in terms of what the person can actually accept.
For example: A suggestion may be very useful. And a mental trigger or other mental problem does not change that, nor give anyone the right to blame you for their problems… But a trigger will prevent the person from accepting otherwise good information, and you cannot quickly fix that with InstaTherapy™. So, as you hinted at, you still want to communicate it in a way that can be accepted even with that. Because your goal is to actually get it across.
But actually, it’s really not your job, but theirs. (The instructor is paid too, no? So where’s your money’s worth?) But that is of no use to help you right there, right then. You need to actually get it across!
I don’t know how the culture in your country is, but I know about the stark difference in this, between my country, Germany, and e.g. the USA, and what effects it has. …
Here in Germany, frankness is the standard modus operandi by everyone, and you either grow some confidence and stability (what we consider growing up) or die trying. But what looks offensive to US-Americans is only superficial, as we are well-meaning, usually want things to be better, and don’t even think about putting somebody down (unless we are clearly angry). …
By contrast, in the US, everyone is always nice, which is of course nice, and everything is wrapped is soft cushions and cotton candy. But in my experience, this is often only superficial, and behind the scenes it might be “basically war”, and criticism is very often seen as purposefully hurtful, so everyone either becomes very careful in how they express themselves, or dies trying. (In its most extreme case, it enables modern people to bully by becoming “offended”.)
US-Americans probably find our culture as bewildering as we find theirs.
So of course, the approach depends on the culture of who you’re dealing with, and cannot be answered fully in general for a specific person. (In short: Empathy, for them as well as you, and getting to know the person as well as you makes things easy.)
In the end, I wouldn’t shy away from giving any criticism that will improve things, but ALSO rather focus on expressing it in the right way. No Either-Or. but an And!
That way you get the best of both worlds. It takes empathy and brain power of course. But you literally are currently doing exercises for your brain power, so… :)