A card floats into the margin from its anchor's paragraph or list item. A heading or a table cell can't reach the margin, so a comment or suggestion there has no card. Comment on the heading from the paragraph under it.
Incorrect
Sign in
Section titled "Sign in"Enter your email.
## Sign :suggestion[in]{from="on" note="The button says Sign in."}
Enter your email.Correct
Sign in
Section titled "Sign in"Enter your email.The heading changed from Sign on, to match the button.
## Sign in
:comment[Enter your email.]{note="The heading changed from Sign on, to match the button."}