Unable to generate test for apps not in the benchmark

[Prefest2018]

Hi, I am trying LAND to test some other Android apps, such as the famous AmazeFileManager. However, after I configured all the environment required and launched the GUI panel of LAND, I have been stuck in the "Instrument" step with the following logs:

-----------------------> Instrumenting <-----------------------
Instrumenting for methods:  +
Instrumenting for keys:     +
Instrumenting for branches: -
Instrumentation time: 874ms
--------------------------> ! DONE ! <-------------------------
I: Using Apktool 2.3.0
I: Checking whether sources has changed...
I: Smaling smali folder into classes.dex...
I: Checking whether resources has changed...
I: Building resources...

I cannot found any stubbed versions of the app AmazeFileManager and the "Profile Generating" Button is still unenabled, and therefore we cannot start the GUI exploration. What should I do? Would you please help me?