This Excel add-in demonstrates a known issue with using custom functions inside conditional formatting rules. The add-in creates custom functions and applies conditional formatting to cell C1, but ...
ClosedXML.Parser.ParsingException: 'Unable to determine token for '~*' at index 0.' at ClosedXML.Parser.FormulaParser`3.Formula() at ClosedXML.Parser.FormulaParser`3.CellFormulaA1(String formula, ...