Table column has non-standard date format, but Excel won't recognise date for that format

Problem
We have an Excel table where the column's category is date and the type has been set to "dd.m.yy"

Excel would recognise any new dates typed into the table of that format as dates.

At some point this stopped happening and now dates must be typed in, in the format "dd/mm/yy" at which point, Excel then formats them as "dd.mm.yy".

Why will Excel no longer recognise my date formats?

Set-up

• Excel Version: Microsoft Office Professional Plus 2010


• Windows: 10


• File type: .xlsx