Exporting document library and importing on another site collection messes up the tagged columns

I have several document libraries on a site. I have created a new site collection to host these libraries. so I export these libraries via Central Admin and then import them via Powershell and they import ok and all the columns and views are there also. The odd thing is that some of the Managed metadata columns show incorrect tags that should not exist on those columns.

The tags that are displayed on the column after exporting the library do not exist on the term store under the data category term set.

I have deleted the exported library several times and exported to other site collection as well and same result. I have reset the index and run the full crawl also and the original library still remains the same but when I export it and import to other site collection, same issue.

I have about 25 Libraries to export and a few of them have this issue and it is quite worrying as they lots of data on them with tags. Any one has any ideas??