We often found our lab data showing 0 CLS but then big shifts coming through in our field data.
As CLS continues increasing as users scroll around pages or interact with your site these shifts will not show up in lab data.
As pneenan mentioned using a performanceObserver is your best bet.
You then scroll around our page keeping an eye on the Chrome dev console.
I’ve more detailed instructions on this here
I just realised that you gave a link to your website. I believe the problem elements are your quicklinks in the bottom right hand corner on mobile. They are expanding and contracting when a user scrolls on the page causing LayoutShifts.
Hope this helps!