Hi Adam,
What’s the result if you try it with different team project?
Please try to clear TFS client cache and try again. (e.g. C:\Users\v-stache\AppData\Local\Microsoft\Team Foundation\4.0)
On the other hand, based on the
description, TFS Integration Tools were designed to work with Team Foundation Server 2012 and earlier. Use of these integration tools with TFS 2013 and 2015 may cause errors. So for integration tools with VSTS, it may cause errors.
As far as I know, there isn’t other official tool to migration work items, I suggest that you could submit user voice
here for the feature of migration work items or other.
Regards
Starain
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