I have searched here and have seen this addressed - whether it is black gaps or the playback head showing "the previous frame instead of the next one." I also know it's fixable - whether you do it manually cut-by-cut or use a script, "close gaps," etc.

My question is, if all of the media is the same frame rate as the project from the very beginning, and quantize isn't even visible to be clicked "by accident" at any time - what causes this to begin with? And is there any way to keep it from happening? It can't be exclusively one particular way of adding clips to the TL, as I will trim both on the timeline and in the trimmer.

It's almost as if everything was nudged by a half a frame. And this isn't a "recent thing," as it explains why, over the years, sometimes when you bring two clips together for a hard cut, it will give you a 1-frame crossfade (or it will kill a "fade out" butt up against a "fade in").

Is this just a "natural" phenomena at times as a result of the whole 29.97 or 23.98 vs 30 & 24 thing?