Sudden Vuforia initialization error

My team has been using the build I've made 2 months ago without any problems until few days ago.  All of a sudden the build that has been installed on 4-5 devices fail during the initialization.  The init code is from SampleApplicationSession.mm file without any modifications other than the license key.  Here's the code:

// mVuforiaInitFlags = GL_20

Vuforia::setInitParameters(mVuforiaInitFlags,"MyLicenseKey");   // Vuforia::init() will return positive numbers up to 100 as it progresses // towards success.  Negative numbers indicate error conditions NSInteger initSuccess = 0; do {   initSuccess = Vuforia::init();   NSLog(@"%d", initSuccess); // log below } while (0 <= initSuccess && 100 > initSuccess);         if (100 == initSuccess) {   // We can now continue the initialization of Vuforia   // (on the main thread)   [self performSelectorOnMainThread:@selector(prepareAR) withObject:nil waitUntilDone:NO]; }

initSuccess return -1 which translates to just a default error.

I tried to log initSuccess:

2016-10-04 11:28:37.397134 aria-demo[3234:494344] 50 2016-10-04 11:28:37.397223 aria-demo[3234:494344] 50 2016-10-04 11:28:37.397359 aria-demo[3234:494344] 50 2016-10-04 11:28:37.398252 aria-demo[3234:494344] INFO/AR(3234) 2016-10-05 11:28:37: Vuforia SDK version 6.0.2 2016-10-04 11:28:37.475353 aria-demo[3234:494344] Rendering mode set to: OpenGL ES 2.0 2016-10-04 11:28:37.476164 aria-demo[3234:494344] -1

It doesn't make sense that Vuforia just started failing on all installed devices.  I thought it was a license issue (Development license), but when I tried to make a new one, it still failed.  It's not iOS 10 issue because all iOS 9 and 10 devices fail.

Any ideas?  Thank you.