FullText Search does not work after upgrade

The most likely cause for that is that you failed to successfully migrate the work item index files. You should check all the teamserver.properties files for where the index files are, and move them to a location outside of the server folder.

After making sure you know where the index file locations are and that they don't get lost during upgrades, you can run the repotools to recreate the index files. I think repotools-ccm -reindex recreates the work item indexes.