Inconsistent behavior when testing iOS App that contains WKWebView with Appium

Question

I am creating automated tests for an iOS app that uses WKWebviews to display some data. The user types a query into a native text field and results are displayed inside the webview. The problem is that I got inconsistent behaviour when checking some expected structure in the HTML.

Here is the HTML I am expecting:

<div id="results">
    <div class="frame">
        <div class="card">
            // here my data
        </div>
    </div>
</div>

In Appium I check the very simple case that these three divs exist as the follows:

it("should display results inside the web view", function () {
    return driver
    .waitForElementByName("Address and Search")
    .sendKeys("search query")
    .sleep(1000)
    .contexts().then(function (contexts) { // get list of available views. Returns array: ["NATIVE_APP","WEBVIEW_1"]
    return driver.context(contexts[1]); // choose the webview context
    })
    .waitForElementById("results", 60000)
    .waitForElementByCss(".frame", 60000)
    .waitForElementByCss(".card", 60000)
    .sleep(3000)
});

Every time I run the test I get different results: sometimes it finds all elements, and sometimes it find only the first element (waitForElementById), then fails to get any further elements.

Here is my configuration:

exports.ios93 = {
    browserName: '',
    'appium-version': '1.4.13',
    platformName: 'iOS',
    platformVersion: '9.3',
    deviceName: 'iPhone 6',
    app: undefined // will be set later
};

I tried to solve the problem by doing the following:

Adding delay after switching to WEBVIEW as follows:

.context('WEBVIEW_1')
.sleep(25000)

Changing the window as follows:

.context('WEBVIEW_1')
.windowHandles()
     .then(function(handles) {
         driver.window(handles[handles.length-1])
     })

but this didn't have any effect.

Note that the Android version of the app does not have all these problems when testing with Appium.