In the https://help.liferay.com/hc/en-us/articles/360017902892-Breaking-Changes documentation, I did not observe
LPS-71850 listed. LPS-71850 introduced a behavior in which certain input fields were replaced to use AlloyEditor fields instead. AlloyEditor, by default, adds a <p> tag to every editable field and considers the behavior as intended and inherent part of AlloyEditor.
This prevents HTML tags from rendering in the summary field of Web Content.
Prior to 7.1 HTML tags were rendered in the summary field of Web Content.