I’m still in 4.12.4, but for me the issue was caused by a stale dependency in GearVR_APL.xml
If you force the OSIG files to be removed, GearVR_APL.xml adds an entitlement check to GameActivity.java. Unfortunately, that entitlement check uses com.oculus.svclib, which Oculus removed from their mobile libs back in June or so.
To get rid of the stale dependency, go to GearVR_APL.xml and comment out this line:
com.oculus.svclib.OVREntitlementChecker.doAutomatedCheck(this);
Alternatively, you could just disable the “remove OSIG files” option and manually delete all the OSIG files in UE4\Engine\Build\Android\Java\assets before making a build.