CKEditor Knowledge Base Article insert horizontal line function does not draw a line

• Type: Regression Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: Master
• Fix Version/s: 7.3.5 CE GA6, 7.3.10 DXP GA1, Master
• Component/s: Alloy Editor, CKEditor
• Labels: None
• Fix Priority: 3

Steps to Reproduce:

1. Go to Site Menu > Content & Data > Knowledge Base
2. Add a new Article
3. copy a block of text from https://loremipsum.io/generator/?n=5&t=p
4. Paste in CKEditor.
5. Click anywhere in the text block
6. Click on Insert Horizontal Line button

Expected Results:
There should be a horizontal line in between the space

Actual Results:
There's no line, instead it creates a space in between 

Environment:

Tomcat 9.0.33 + MySQL 5.7
Portal master GIT ID: 7880f345288eea44d4763f8531665f1c4210a07d