Fixed element behaves static after interaction

I’m building an off-canvas menu. The menu (and general UI) is fixed on scroll. After the menu has openend the UI class appears to be static again. Does anyone knows what’s happening here?

https://preview.webflow.com/preview/saus?utm_medium=preview_link&utm_source=designer&utm_content=saus&preview=6c604cea1b0df8701764771d485a0da1&pageId=5d8caf854b00517019972153&itemId=5d8caf854b005132ed972144&mode=preview

Live preview here: Burgerkracht Limburg met Saus


Here is my site Read-Only: LINK
(how to share your site Read-Only link)

I have another example of this behaviour. It would be great if someone picked this up.

This is the other example: https://ingeborg-meulendijks.webflow.io/projects

https://preview.webflow.com/preview/ingeborg-meulendijks?utm_medium=preview_link&utm_source=designer&utm_content=ingeborg-meulendijks&preview=ed80cb1064f1f167035ef3a3076d6e52&mode=preview