I start a new, Winforms .Net Framework 4.7.2 project.
I add the radBarcode to the form, a sample QR code is shown.
I change the Symbology-property to DataMatrix, the sample picture of the barcode is cleared and no barcode is shown. This is also the case when I change the Symbology-property via the control smart menu/tags

And here comes the point: I always inserted my value for the barcode in the Text-property and not in the Value-property (my fault). After playing around and reading the docu I realised that I need to set the Value property. If I do this via smart menu/tag It works fine.

But why does the Value property get cleared by changing the Symbology-Property? If there could be any conflicts between different barcodes, wouldn't it be better to show some infobox, that the value is incompatible to the selected symbology?

The issue can be reproduced by adding a RadBarCode to the form and setting its value this way:

this.radBarcode1.Value = "https://docs.telerik.com/devtools/winforms/introduction";

The barcode cannot be read with the property set to false.

Workraound:
Telerik.WinControls.UI.Barcode.Symbology.EAN128 code39Extended1 = new Telerik.WinControls.UI.Barcode.Symbology.EAN128();
code39Extended1.Checksum = true;

Workaround: set to the ForeColor to the RadBarCodeElement
this.radBarcode1.BarcodeElement.ForeColor = Color.Red;