Hey @raachotrekkers
Just my input in case this works for you since you are having the same error I had. My issue was with the Yoast plugin, it was adding a second FAQPage schema.
What I did was change the FAQ default Page Type to Web Page, not FAQ page and the Article Type to None
To do this go to your Yoast plugin settings:
SEO > Search Appearance > Content Types > scroll down to FAQs > Schema Settings > Default page type : select Web Page
Default Article type: select None
If you have it like this already the error might be only on specific FAQ pages, you can see which pages on the Google Search Console, go directly to those pages within the FAQ plugin and change the Yoast settings there.
Hope this helps