Cloud connection failure. token Failed (status code 503)

I’m suddenly getting this showstopper when my cloud SDK app on iPhone tries to connect to Particle cloud in order to read data from Asset Tracker Electron.

loginWithUser https://api.particle.io/oauth/token Failed (status code 503): {
error = “server_error”;
“error_description” = “server_error”;

ANOTHER OF MY APPS, THAT USED TO WORK, NOW REPORTS THIS:
getDevices https://api.particle.io/v1/devices Failed (status code 400): {
error = “invalid_request”;
“error_description” = “The access token was not found”;

How do I correct my access token?

App is running on iPhone with iOS10.

I can use iOS Particle app to logout and log back in, and to read the same data from cloud that my SDK app can no longer read.