Steps to replicate the issue (include links if applicable):

Editing source code when using Timeless skin + 2017 Wikitext editor + built-in syntax highlight function. The problem disappeared when I switched to Vector or 2022 Vector skin.

What happens?:

Wrong relocation of cursor typing position. The problem started a month ago, and before that, everything worked fine.

What should have happened instead?:

Correct relocation of cursor typing position.

Software version (skip for WMF-hosted wikis like Wikipedia):

All Wikipedia projects (e.g. English, Chinese, Cantonese....). But works fine in Wikimedia Commons.

Other information (browser name/version, screenshots, etc.):

I have this issue on both my iPhone, Mac and Windows browsers. Same in safe mode.