try to start by adding this -dontobfuscate to proguard file and just see if it will workd what it will do is just not obfuscating names but the code will still be optimized but it is not ideal just use it for debbuging .

also try adding @SerializedName("idLinea")and @SerializedName("nameLinea") which should prevent the varaible's name's from being changed in the serialization.

take a look at this article android proguard and serialization