New Outlook won't search for old e-mail

Hello, 

I have someone that has been having issues with their outlook account. Originally the issue persisted in the Classic Outlook. They would search for an old e-mail sent from a specific user, and they would be prompted by an error message saying "it looks like there's a problem with your network connection - let's check on your computer instead". Which feels to me that it struggled to search the 365 exchange server first which prompted the error message - however, the email was able to be found as it is stored locally. 

I re-installed outlook. I rebuilt the search index. I added a DWORD key in the registry 'DisableServerAssistedSearch' within 'HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Search\DisableServerAssistedSearch' and set value to 1. 

This prevented the error message from cropping up whenever the email was searched for. 

However, now when the same search is attempted on the new version of the outlook - it doesn't do anything other then display an error message simply saying "Your request can't be completed right now". 

Is there a fix for this? It's quite annoying for anyone wishing to use the new version of the outlook.