Hi @dtaraboletti ,
From your description, you want to adjust the Excel Web Access web part height to fit the content. You set the value to "Adjust Height to Fit Zone",but this setting keeps reverting back to the fixed height of 400 pixels.
I could reproduce your issue in my environment.
As a workaround, you can use CSS code to adjust the height of the Excel Web Access web part. You can add a Content Editor Web part into the page, then add this code below into the HTML source of the content editor web part:
<style>
#WebPartWPQ2 {
height:auto !important;
}
div[id$='sheetContentDiv']{
height:auto !important;
}
</style>
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