Google Sheets – QUERY Changes Time Format Issue

I couldn't find the trick for the real date cell to work yet, but you could have a work around if nothing else by adding the the single quote (') before the date in a format: YYYY-MM-DD in the Q4 cell.

That single quote means that the it will be parsed as string.

I think you're right that this is a date format issue.

On a quick look, when you test 27/07/2019 > 01/08/2019 the result is TRUE
However when 01/08/2019 > 5/08/2019 is tested you have the expected FALSE
When =DATEDIF(L8,L9,"d") is tested or Date A - Date B there's the expected 5 result.

So when I input the data myself (27/07/2019 > 01/08/2019) there's a false. That is the good behavior.

You just need to format your dates on column D. Take D column and use a different date format with the More Formats option.

Here's the mess I made to find out.

Another way to format this column:
Try this formula =DATE(YEAR(D1),month(D1),day(D1)) where D1 is obviously the date with a weird format.