Alex, you are right. I should have looked at the source instead of relying on your screenshot from lighthouse. Congratulations, you have found a bug. I spent some time trying to replicate your issue.
Webflow, under certain circumstances, adds a shared ID to multiple elements. Webflow should not add the same ID to multiple elements since the ID is a global attribute that must be unique in the whole document according to the spec.
What Triggers It?
My tests show that when a collection list is set to display:grid and the child collection item has an align-self property set, it triggers the bug. Webflow then creates a unique ID which it assigns to all the collection items. You can confirm this by removing the align-self property. Note: this property doesn’t apply to block-level boxes, and to table cells.
Remove the align-self property from your collection item. If you want to center the heading in the box below the image you can use flexbox with display:flex and justify-content:center
Since this is a bug I moved it to the Feedback: Bugs category.