I've addressed this issue now. We had the same issue on another page so copy pasting my response from there:
This issue occurred while I was adding keyboard navigation support to
our tag popovers as part of our accessibility initiative. It turns out
we're using clip-path to animate the collapsible component here which
creates a new css stacking context. Thus causing the painting order
problem (different stacking contexts don't share the same z-index
context).
I had to disable the collapse/expand animation for now to get rid of
the issue. We will look into alternative animation strategies for a
long term fix but this change should address the immediate issue.