Yeah, that's an actual syntax error... the correct version would be this:
var i;
for( i=0; i<len; ++i ) {But yeah, this is weird... if we're using the exact same runtime to load the exact same file, we should get the same results. (You're using the v1.1 version of the GMS2 source, right?). Maybe it's time to contact Yoyo support about it...
There's one more thing we could try first, though... I'll try importing the GMS1 1.1 source file in the latest version of GMS2 and upload that as a GMS2 1.2 source file, and if there's any issues with the compatibility scripts that should hopefully be resolved by that.