Hi,
I was able to find a relevant error logging:
** Message: 15:25:59.819: Remote error from secret service: org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.secrets was not provided by any .service files
(node:21456) UnhandledPromiseRejectionWarning: Error: The name org.freedesktop.secrets was not provided by any .service files
(node:21456) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 13)
Subsequent google search led me to https://github.com/Foundry376/Mailspring/issues/681#issuecomment-364982754 with the solution being
sudo apt install gnome-keyring
Which then allowed me to save configuration settings. Thanks.