When you download a document with taxonomy fields from site collection A and then upload it again into site collection B, the taxonomy values on the documents might not be set correctly. The values are displayed, but in the wrong column. To prevent this, two steps can be taken by the user:

• After the download, remove the “Document Properties and Personal Information” from the document via the “Inspect” option in Office. When the document is uploaded again, the default values from the new site collection will be used.
• Copy the document from site collection A using the OOTB “Copy To” functionality. Now SharePoint takes care of setting the taxonomy fields correctly.

Some background information: the taxonomy field value is linked to the “TaxonomyHiddenList” of site collection A via the ID in the hidden list. Once the document is moved, the ID remains the same but on site collection B this ID might be linked to another term as the “TaxonomyHiddenList” values can be different.