How to persist suppressedsrc on custom iframes

Vimeo and YouTube videos appear to retain the suppressedsrc attribute even after consent is granted. How can I ensure that suppressedsrc persists on custom iframes? While the src is updated when consent is provided, it reverts back to the suppressed state when navigating away from the page.

<iframe 
    class="_iub_cs_activate"
    data-iub-purposes="4"
    src="https://example.com"
    suppressedsrc="https://someotherwebsite.com"
></iframe>