Hi Ibbe,

The stack trace gives us a clear starting point. The error originates in NPOI's AddExternalRelationship(String target, ...), where the target parameter (a URI) is either null or empty. The call chain shows that ReplaceTextWithText is invoking InsertNewHyperlinkRun, which then fails when trying to register that URI.

There are two plausible scenarios here, and I'd suggest investigating them in this order:

1. The placeholder or surrounding text contains hyperlink formatting in the template.

In Word, it's common for text to carry hidden hyperlink formatting without any visible indication, especially if it was pasted from another source. When OfficeUtils processes the replacement, it may encounter a hyperlink run and attempt to reconstruct it with an empty or missing URI, which would cause exactly this error. To rule this out, open the template, select the area around {Contact.Address_2}, and check whether Word shows any hyperlink formatting (right-click > "Remove Hyperlink" is a quick way to test). If you want to be thorough, you can rename the .docx to .zip, open word/document.xml, and search for  elements near that placeholder.

2. A possible defect in the 5.8.0 deletion path.

I notice your configuration has DeletePlaceholder: true with OutputType: 1. If OfficeUtils 5.8.0 introduced changes to how placeholders are deleted, and the code path for deletion incorrectly enters InsertNewHyperlinkRun with no URI to pass, this would produce the same error regardless of whether there's a hyperlink in the template. Since you mention the issue appeared after upgrading to 5.8.0 and the template itself hasn't changed, this is worth considering. Testing with DeletePlaceholder: false (and an empty replacement text as a workaround) could help isolate whether the deletion logic is the trigger.

As a temporary workaround, reverting to the previous OfficeUtils version should bypass this, though keep in mind there may have been reasons for the 5.8.0 update (security patches, other fixes) that are worth weighing before staying on an older version long-term.

Either way, I'd recommend reporting this on the OfficeUtils Forge component page under the Support tab with the stack trace and your placeholder configuration. If this is a regression, the component author would need this information to address it.

Hope this helps narrow it down.