Hi Sergey.
It is working now with that configuration. Thanks a lot and I´m glad you like the app 
I was having same trouble but i just added a line to my proguard file to tell proguard to keep my model class.
-keep class com.my.package.models.** {*;}
where com.my.package.models is the package of your models.
hope it’’’ help someone and thanks to all backendless support team