Excel don't recognize formulas from closedXML / c#
<blockquote>
  <p>Info: The following code is in a foreach loop</p>
</blockquote>

<p><strong>Works:</strong></p>

<pre><code>indexSheet.Cell("G" + cellIndex).FormulaA1 = "=SUM(A1:A10)";
</code></pre>

<p><strong>Only works, when i type this directly in excel:</strong>  </p>

<pre><code>indexSheet.Cell("G" + cellIndex).FormulaA1 = "=FIND(\"erw\";H5)"; // with Property
indexSheet.Cell("G" + cellIndex).SetFormulaA1("=FIND(\"erw\";H5)");  //with Function
indexSheet.Cell("G" + cellIndex).FormulaA1 = $"COUNTIF(H{cellIndex};\"*\"&amp;$C$2&amp;\"*\")*(MAX($G$4:G{cellIndex - 1})+1)";
indexSheet.Cell("B" + cellIndex).FormulaA1 = $"=IF(ROW()-{cellIndex}&gt;MAX(G:G);\"\";HYPERLINK(CONCATENATE(\"#\";(INDEX(H:H;MATCH(ROW()-4;G:G;0)));\"!B{cellIndex}\");(INDEX(H:H;MATCH(ROW()-4;G:G;0)))))";
</code></pre>

<p><strong>I've checked/tried:</strong></p>

<ol>
<li>Because in stackoverflow exists a similar case: If the language of my functions matching with my excel language (both are english)</li>
<li>I tried if simpler formulas would work like <code>SUM()</code> or <code>FIND()</code> --> (-SUM works, FIND doesn't work )</li>
<li>I typed the formulas directly in an excelsheet (formulas working here)</li>
<li>I tried it outside from the Loop with a hard-coded cell-informations and without the "cellindex"-variable</li>
<li>Checked out the closedXML-documentation</li>
<li>Whit equal signs at the beginning of the formulas and without it</li>
<li>I tried with closedXML Vers. 0.76.0 and 0.80.1 (latest stable)</li>
</ol>

<p><strong>Excel shows me this:</strong>
<a href="https://i.stack.imgur.com/cqLQF.png" rel="nofollow">Picture1</a></p>

<p><strong>And this:</strong> 
<a href="https://i.stack.imgur.com/3c4d3.png" rel="nofollow">Picture2</a></p>

<p><strong>The Linked XML-logfile from Picture 2 contains informations about the deleted parts</strong></p>

<pre><code>&lt;?xml version="1.0" encoding="UTF-8" standalone="yes"?&gt;
&lt;recoveryLog xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main"&gt;
    &lt;logFileName&gt;error035720_03.xml&lt;/logFileName&gt;&lt;summary&gt;Errors were detected in file 'C:\Users\XXX\Documents\Output\CodeBook.xlsx'&lt;/summary&gt;
    &lt;removedRecords&gt;
        &lt;removedRecord&gt;Removed Records: Formula from /xl/worksheets/sheet.xml part&lt;/removedRecord&gt;
        &lt;removedRecord&gt;Removed Records: Formula from /xl/calcChain.xml part (Calculation properties)&lt;/removedRecord&gt;
    &lt;/removedRecords&gt;
&lt;/recoveryLog&gt;
</code></pre>