So I transferred my project from PC to Mac, after using the "collect files" option. Then, when I opened my project on the Mac, everything seems to be alright, except they tell me my "Fade in & out (frames)" effect is missing.
So naturally, I tried the "find missing effects" option as this effect is a standard effect; however, it did not find anything missing.
All of the effects are still on the layer, but they are not doing the effect.
Is there a way I can have all layers find the effect without manually putting on the same effect?
That's not an effect, that's an expression-driven "pseudo-effect" preset, meaning the preset could be missing or something as trivial as a different language setting break the underlying expression. Either way, you have not provided exact system info or version info for AE nor any other details, so we can't even begin to properly diagnose this.