Hey @AlexisFrance welcome to the forum!
Since you didn’t include a “read only link” to your Webflow build it’s tough for most people to help you here. (How to Enable a Webflow Share Link)
I’ve put together a short video though using Chrome developer tools. You can see your elements disapearing on screen and on the right you can see the code changing as we move over the breakpoint.
The important thing to notice is that the code changes from “opacity=1” (visible) to “opacity=0” (not visible) in this time. So your elements are still there you just cant see them.
Without seeing your read only link its gonna be tough to explain why this is happening. I would check the opacity setting at this breakpoint first although I think it’s more likely this is due to an interaction being applied at that breakpoint.
All the best,
Dave