Strange, couldn't get your suggested VBA function to make a difference; though I tried to recreate the issue rather than mess up my fix on the particular issue. I caused an error, but it was always a popup box rather than a cell triangle warning, and the popup wouldn't allow me to put in the wrong data.

Your code in vbaExpress71200.xlsx is the same as mine, other than mine uses dynamic lists so that the data keeps spilling. I don't know if that makes a difference.
In my columns when I type a name into one list, the name comes off the other immediately, much the same as your data dropdowns work. My dropdowns are on another sheet of course, and the filter brings the data to this hidden sheet. The rows are not necessarily contiguous on the other sheet. I noticed that while there are workarounds for filtering a range of columns that are not contiguous, dynamic filtering prefers the ease of contiguous columns. I wonder if breaking contiguity in rows can cause the inner workings to perform differently.

I have lots of wondering... but no time to figure each one out. For now, I press forward. This certainly has been an interesting thread. Thanks

Gary