I'm having to use a template which I did not create and I'm limited in the changes that I can make.
This template uses bottom borders on three levels of Heading Styles - Heading 1 has 1 1/2 pt bottom border; Heading 2 has 1 1/2 pt bottom border; Heading 3 has 1/2 pt bottom border.
If Heading 2 follows Heading 1 i.e. they are line 1 and line 2, the border under Heading 1 disappears. Yet when Heading 3 follows Heading 2, and the weight of the border changes, they both appear (see sample below).
I've tried to update Heading 1 with a heavier bottom border but it hasn't worked.
Another suggestion was made to highlight both Heading 1 and Heading 2 and add an inside border, however, this leads to other issues with spacing After the Styles which I'm unable to change.
I'm out of ideas, have you got any?