error behaviour: elements change

The newest Update breaks my site.

Linked elements change, in example this:

<div class="wp-block-buttons is-layout-flex wp-block-buttons-is-layout-flex">
    <div class="wp-block-button">
        <a class="wp-block-button__link wp-element-button" href="https://econgood.ch/ueber-uns/gwoe-kurz-erklaert/#werte">Menschenwürde</a>
    </div>
</div>

in to

<div class="wp-block-buttons is-layout-flex wp-block-buttons-is-layout-flex">
    <a href="#" class="custom-btn"></a>
    <div class="wp-block-button">
        <a href="#" class="custom-btn"></a>
        <a class="wp-block-button__link wp-element-button" href="https://econgood.ch/ueber-uns/gwoe-kurz-erklaert/#werte">Menschenwürde</a>
    </div>
</div>

The page I need help with: [log in to see the link]