Video Clip at 0% opacity still "flashes" visible

I have a video clip that says it's at 0% opacity, but when the playhead hits the first frame of the clip, there is a visible jump or flash as the image clicks on. What might be causing this?

I'm working on a montage sequence that involves multiple layers of video clips dissolving into each other at various rates. Each clip starts at 0% opacity and is keyframed to rise to, say, 50% opacity and then drop back to 0%. At some points, there are four or five clips stacked on top of each other, all at different opacities. Some of these clips work exactly as intended, smoothly fading into and out of the image. But a handful of them have this "flashing" issue, where the start of the clip adds a sharp change to the image, even though the layer says it's at 0% opacity at that frame.

I'll admit I do not yet fully understand the different opacity blending modes (I promise to study up soon,) but changing between a variety of blend modes did not solve the problem.

At one point while trying to diagnose the problem, I was able to narrow it down to a speed effect as the cause. By nesting the clip, moving the speed effect inside the nest, and then applying the opacity keyframes to the Nested Sequence, the clip no longer "flashed" when the playhead hit the start of the clip. However, this workaround only appears to work on some of the problematic clips, while others still exhibit this problem even after nesting. That feels like a clear red flag that it's a technical bug, but the lack of similar forum posts along with my own sub-proficient understanding of opacity tells me the problem exists on my own end. Please help!