Excel autofill combination of letters and numbers

Hi,

I noted the reply to your query and wonder if you can help me?

 I input a string, say 1 2 3 4. 

When I drag the handle down, the values all revert to 1 which keeps on repeating a column of 1.

Same with a date string. I enter 28/12/2018 and then 29/12/2018 etc,.

When I drag down, the dates all are 28/12/2018.

This was working great and has only just started going awry.

Have you any suggestions?

Thanks