How to autofill the same date down a column in Google Sheets?

I'm using google sheets to work on a spreadsheet, there are values in columns A-M. In Column A, there is a date. This date changes about every 400 rows or so (it doesn't change by a consistent number or after a consistent # of rows).

I like to use autofill to quickly put values down a column, but for whatever reason, Google Sheets refuses to autofill down to the last row with a value in it.

All I want is for the same date (by highlighting two cells with the same date) to autofill down (by double clicking). I've done this before countless times for other data types, I don't understand why I have to drag the value down instead of just double clicking. I know this sounds like a really basic question, but it's adding a lot of time to something that could be completed very quickly and I haven't figured it out yet.

Thanks in advance for any answers

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