I was just working with a customer that had to restore TFS using a VM snapshot as they did not have SQL backups. The length of time on the rollback was significant and after the rollback, the users began running into TF400667 (Work Item Type Definition Error) issue updating work items having an area or iteration created after the rollback date. Meaning, if the VM rolled back the data to Monday, all areas or iterations created Tuesday on were encountering the issue when updating the work item.
The customer removed the problematic areas and iterations and recreated them with the exact same spelling within both the web client and Visual Studio. Even after the updates, the customer was still encountering the same error message when editing a work item with the new areas of iterations.
During the problem isolation process, we created new areas and iterations (not having the same names as the problem iterations and areas) and noticed the areas and iterations were not appearing in the work items (new or edits) from within Visual Studio. However, the new areas and iterations were appearing in the web client. So, if the areas and iterations were appearing in the web client, it must mean they are being saved to the database and something was amiss in Team Client for Visual Studio.
For the resolution of the issue, we deleted the TFS cache on the user's workstation, closed and reopened Visual Studio and the new areas and iterations appeared!
Local Cache Location: C:\Users\<UserNm>\AppData\Local\Microsoft\Team Foundation\<Version of TFS Cache>\Cache
The user's local TFS cache was out of sync with TFS and the deletion and downloading of a new cache synchronized the environment. Must have been due to the way the customer used the VM snapshot rollback instead of a SQL restore using the TFS restore utility.