When copying list items which contain an Enterprise Keyword field, due to limitations, all terms in the field that don't exist at the destination will be copied as keywords. This also applies to terms placed under a term set within the managed metadata infrastructure at the source which will be copied as keywords at the destination.

The warning should appear on a given list item, for example: "Property 'Enterprise Keywords': One or many terms in the Enterprise Keywords field are placed under a term set within the managed metadata infrastructure at the source. Due to limitations, the following term(s) were copied as keywords at the destination: 'Red', 'Blue'".

The warning occurs because at the source, some terms in the Enterprise Keywords field are terms from the managed metadata infrastructure. Sharepoint does not provide information from the list item field on the location of the term(s) within the managed metadata infrastructure. Therefore, when copying list items, Sharegate will copy all terms in the column as keywords at the destination.

If you want to keep using the same managed metadata infrastructure, prior to copying the list items with Enterprise Keywords, copy all related managed metadata term sets to the destination using Sharegate. Then, when copying your list items, Sharegate will use the copied terms at the destination to populate the Enterprise Keywords column of the list items at the destination.