Well, getting a "complete" list of all the causes is most likely the impossible dream! By your own admission, there are varied causes, and I'm sure we haven't actually properly identified the root cause of many of the interference issues. For instance, Joe posted a unique issue that I had never heard of before! The TMCC being a separate layout and not connected to the tracks with DCS is a new one, I had never heard of that issue before!
Whoa.... I am very sorry here GRJ.
I traced the issue to a ground wire that connected my upper 3 rail loop to the rest of my two rail. The TMCC signal was connected thru an internal connection on something, that I now forget. I believe it was the Z4000? The 3 rail had a separate TIU so that wasn't it.
It drove me nuts and I only shared the video to show it happens. Nothing else was dragging the signal down. NO TMCC engines on the rails.
Later on when they became available, I had two more PH180 bricks (on order for a year?) so I could separate the Z4000 from my outer O scale 2 rail loop.
Since I got my 2 rail MTH Bigboy, I connected the Z4000 again for higher voltage and power. So I have to remember not to plug in my TMCC base!