I noticed that there are some problems replacing image target. I mean:
1) Create trackable and use it in Unity scene
2) Create another trackable and import new package (with single trackable) in Unity scene
3) Make sure scene uses new trackable
4) Build -> Result: AR doesn't work. I can see an exception that my new trackable couldn't not be found.
I noticed that config.xml contains both new and old trackable. Removing old trackable from config.xml fixes the problem.