I was debugging a user's game and I saw those errors too. I don't remember if it was before or after I updated to your latest release. I made some corrections though, and they went away sooner or later.
nme.JNI -> openfl.utils.JNI
And this one is pretty tough to catch, but there's an nme reference in one of the JNI strings. Should be:
startChartboostAndroid = JNI.createStaticMethod("com/rob1221/MyChartboost", "startChartboost", "(Ljava/lang/String;Ljava/lang/String;Lorg/haxe/lime/HaxeObject;)V", true);
Finally, in MyChartboost.java:
org.haxe.nme.* -> org.haxe.lime.*