If tests do not show in Grid View, this could be an issue with the snapshot isolation or the LQM Updater within the database.
Tests get deleted while the LQM updater is running due to some invalid test plan node-ids in the project history (TM_ProjectHistory) of the imported project. The LQM updater uses this project history to find out which tests have been deleted and then removes the tests from the LQM_Tests table.
This will prevent some tests showing in the gridview even when they are within the list view.
To view the tests again in Grid View, use the following steps:
Before executing the queries, create a backup of your database!