moshi: When using MoshiConverterFactory in retrofit, the first call blocks main thread

I am using the MoshiConverterFactory in an Android Application written in Kotlin in combination with Retrofit. The first call to retrofit’s enqueue does not return directly like expected, but takes between one and two seconds to return blocking the UI thread and skipping up to 100 frames.
The problem only occurs when using Moshi, with Gson as Adapter Factory the first call takes longer too, but only around 150ms.

The code I’m using is:

val time = measureTimeMillis {
    val call = geocodingApi.searchByName("Berlin")
    call.enqueue(object : Callback<GeocodingResponse> {
        override fun onResponse(call: Call<GeocodingResponse>?, response: Response<GeocodingResponse>?) {
          // some code
        }

        override fun onFailure(call: Call<GeocodingResponse>?, t: Throwable?) {
          // some code
        }

    })
}
Timber.d("searching by name took $time ms")

The geocodingApi is initialised in the constructor of my class as follows:

val loggingInterceptor = HttpLoggingInterceptor(HttpLoggingInterceptor.Logger { Timber.d(it) })
loggingInterceptor.level = HttpLoggingInterceptor.Level.HEADERS

val client = OkHttpClient
        .Builder()
        .addInterceptor(loggingInterceptor)
        .addInterceptor(GoogleApiKeyInterceptor())
        .build()

val retrofit = Retrofit.Builder()
        .baseUrl(BASE_URL)
        .addConverterFactory(ScalarsConverterFactory.create())
        .addConverterFactory(MoshiConverterFactory.create(Moshi.Builder().add(KotlinJsonAdapterFactory()).build()))
        .client(client)
        .build()

geocodingApi = retrofit.create(GeocodingApi::class.java)

The logs look like this:

searching by name took 1864 ms
searching by name took 3 ms
searching by name took 4 ms
searching by name took 2 ms

I created a sample application to verify the behaviour without my app code: https://github.com/Phoca/KotlinRetrofitMoshiTest

Thanks for investigating!