The problem concerns a situation in which on the same page is a regular text and bold / italic (.otf font). At the end of the page appears undesirable gap (page 1-3) [1]. The case concerns a line-height.

However, the problem does not occur in a situation where on the same page is only a regular text (page 4) [2].

I use TexGyre font [3][4].

Testcase:
https://codepen.io/bea41659/pen/wgPLdw



[1] http://imgur.com/4b2RAco
[2] http://imgur.com/g8aEIVE
[3] http://imgur.com/QI65Hwj
[4] http://www.gust.org.pl/projects/e-foundry/tex-gyre/termes

Perhaps the regular and bold/italic variants of the font have slightly different metrics. You could try this:

p { line-stacking-strategy: block-line-height }

This will use the line-height specified on the paragraph instead of on the inline element.