Why suggestion format randomly is not applied correctly?

Why when I format a suggestion in a comment, the line is not formatted correctly and furthermore it happens randomly?

I have written a suggestion using the button in the format control bar and it looks like this:


But when I see the preview or save the comment, it looks like this:


What I expect is something like this:


Furthermore, sometimes the preview looks very fine but when I publish the comment, the suggestion appears wrong.

Version I’m using: GitLab Enterprise Edition 12.10.0-pre