I am using a simple UDF in a module:

Option Explicit
Function GetFormula(Cell As Range) As String
GetFormula = Cell.Formula
End Function

This UDF is only used in a conditional format to let me know if someone has
replaced the default formula in a cell with a hardcoded value.

When I open the workbook, Excel seems to forget to initialize the UDF and
the formats are not shown. If I open the module and make a change to the
code or use the function regularly in a cell then suddenly all the
conditional formats start working.

Any thoughts on how to make this more robust so it works as soon as I open
the workbook?

Thanks in advance,