@Cookie8 there is a property called flat which you can use to turn of the translucency property.

For example,

<ActionBar title="Test" class="action-bar" flat="true">
</ActionBar>

And then there is no need to use the native property in the code behind

const createViewModel = require("./login-view-model").createViewModel;

function loaded(args) {
    console.log("LOGIN-PAGE <-> loaded > start");
    const page = args.object;

    page.bindingContext = createViewModel();
    console.log("LOGIN-PAGE <-> loaded > end");
};
exports.loaded = loaded;

function navigatedTo(args) {
    console.log("LOGIN-PAGE <-> navigatedTo > start");
    const page = args.object;
    console.log("LOGIN-PAGE <-> loaded > end");
};
exports.navigatedTo = navigatedTo;

@NickIliev Thank you very much for your tip, however, if I use the flat property approach only, I will not have the vertical line on the bottom of the actionBar.

This is the result of using the flat property only:

And this is the result of using the translucent property:

Do you have any suggestion to handle the display of the actionBar's bottom line when using the flat property?

Thank you very much.

@Cookie8 the flat property is, in fact, removing the translucency, the "shadow" and the elevation and this is its main purpose to "flatten" the ActionBar.

@NickIliev Yes, I understand the purpose of the flat property and find it's very good to know it - Thank you again for the hint.
But unfortunately in my case the flat property won't be an alternative to the translucent property since I need the native look&feel of the ios navigationBar in my app.
I can live with the current behaviour of the translucent property for my further development, however, in my opinion it's a bug. Or am I wrong?
As I'm pretty new to the NativeScript community I'm not sure what to do now, to 'get the bug fixed' eventually. Do I need to report the issue somewhere else?

@Cookie8 thanks you for reporting this issue - here is the right place for posting a bug report. We will investigate the case and post any related information here

I would like to note that I have run into an issue with the flat property as well, where all I need is the translucence set to false. Putting a SearchBar component within the ActionBar forces the ActionBar to grow a bit. When transitioning between pages, this growth is a smooth transition when flat is set to false, but looks choppy when flat is set to true. Trying to set translucent to false on the loaded event on the ActionBar for every page causes the ActionBar to switch back to translucent during the page transition, before switching again back to non-translucent.