Shared Realm on Kotlin Android Queries returning null always

I am using realm kotlin android sdk for my app and using shared realm configuration. When I do any query I returning null always while matching data exists in database

 val userId = app.currentUser!!.id
        val data = realm.query<User>("userId == $0", userId)

above code always return null. Below is config code

 sConfig = SyncConfiguration.Builder(app.currentUser!!, setOf(User::class))
            .initialSubscriptions {
                // Define the initial subscription set for the realm ...
                add(realm.query(User::class,"userId == $0", app.currentUser?.id),"user",true)
        realm =

Sync is enabled on backend UI. I can fetch current user custom data like below

                val data = app.currentUser!!.app.currentUser!!.customDataAsBsonDocument()?.toJson()

but when I try to lookup same user in db it returns null. I also tried giving hardcoded db id but still not luck. Am I missing something?