The workaround is to turn Modern Authentication off for the clients that are experiencing the issue.
Do this by by implementing the following registry key (DWORD (32-bit) Value) after closing Outlook:

HKCU\SOFTWARE\Microsoft\Office\16.0\Common\Identity\EnableADAL

Setting this key to 0 disables Modern Authentication within the Outlook client. No reboot is required.
After opening Outlook back up, you will be greeted with the basic authentication password prompt. After entering the user credentials and opting to have them remembered, the clients have remained connected.