Another thought: Low flow, summer temps (pushing into upper metabolic efficiency tolerances), and fewer emergences can have trout hunkered down. You might be describing trout huddled in summer low flow habitat and not terribly active. You may also be describing some cruising and bottom gleaning type feeding, common in low flow, which is darn tough to cover.
FF isn't easy as trout are not always gung-ho feeders, we don't always know what they are recognizing as food (how it should look and act), and finally we are not providing real food at all. It seems an easy stretch to say that trout want to eat and we want to feed 'em. But it's not nearly so simple. Summer can make that quite apparent.
Observe, take advantage where you can, and continue to refine your technique. Smaller flies, finer tippets, NO micro-drag, and watching conditions, activity, opportunities like a hawk are the keys. A couple other options: Move! Forget that water (until conditions change for the better –flow and temp mostly) or fish ‘em at night (this time purposely employing macro-drag LOL). Try fishing the riffs -try wets, or a streamer across current; active flies can help when the water's warm. In looking for new water search out springs, head upstream into headwaters. You might be shocked at how many happy bug-eaters have packed into such havens.
Once while perusing a local creek I stumbled on a small spring fed feeder channel -obscured by towering willows- that was 10degF colder than the main stem. Trout were on feeding stations all up and down it, rising happily as if it were spring time, while the main channel appeared nearly lifeless for the mile or so I'd hiked it. (The story is MUCH more amusing but I've got to get back to work here).
Ah...one more thing of interest: In really high temps trout can get... weird. A few times, in 80F water, I've seen them bust on dry flies repeatedly but not take. They appear to be taste/tactile-testing (jaw swiping) with closed mouth. They do so frenetically, and repeatedly, as if impulsively. At that point it's best to leave 'em be, sorta like you might do when Grandpa gets that strange faraway look and yells out "Mabel!!" and then, "Who the hell 'er YOU!!"