Update: This is happening only when replying to the first comment of that page it seems. Also the highlight is appearing in an unexpected position.

It's caused by [[Category:Test]] at the end of the first comment, after removing it the reply goes to the right place: https://en.wikipedia.beta.wmflabs.org/w/index.php?title=User_talk:RYasmeen_(WMF)/sandbox&diff=next&oldid=471878&diffmode=source

Regression caused by ae920b831f117c0ad4b5e29c006188cda46ca09f. Looks like we need to have different treatment for <link> nodes representing TemplateStyles, and <link> nodes representing categories.

Change 658483 had a related patch set uploaded (by Bartosz Dziewoński; owner: Bartosz Dziewoński):
[mediawiki/extensions/DiscussionTools@master] Handle category links at ends of comments affecting indentation

https://gerrit.wikimedia.org/r/658483

Change 658483 merged by jenkins-bot:
[mediawiki/extensions/DiscussionTools@master] Handle category links at ends of comments affecting indentation

https://gerrit.wikimedia.org/r/658483