Many have had their Outlook 2016 search fail. MS seems to be ignoring the problem… I have had no search for weeks after rebuilding the index and other remedies.
https://answers.microsoft.com/en-us/msoffice/forum/msoffice_outlook-mso_win10/outlook-2016-something-went-wrong-and-your-search/a6c8c767-9662-4358-94a7-90091c864a27?page=6&msgId=dbfd3715-eb97-4fa4-bcee-97ac7f4e023e