I've had this happen on two machines and I can't figure out if it is a setting somewhere that was mistakenly turned off at some point.

Normally if you enter 08/09/2019 into a cell and press enter, excel will automatically see it as a number. We can help this along by setting the format to that matching type and entering the same thing.

My problem
  1. Enter 08/09/2019 into cell A1
  2. In cell B1 enter =IsNumber(A1)
  3. Result should be True, but it comes up as False instead

Automatic formula calculation is turned on.
Formatting is set to date for the cell.
Fresh reboot with no other excel process running

Any ideas what the trouble could be?

Thanks,