Steps for anyone to reproduce the issue

1. Add a new Chrome user and switch to it.
2. Install UBO.
3. Add a single custom RegExp rule /^https?://(?:\w+[.])?youtube[.]com/user/julica138(?=[/?#]|$)/
4. Load this page: https://www.youtube.com/user/julica138
5. The page is not blocked by the RegExp rule.

Your settings

• OS/version: Windows 7 SP1
• Browser/version: Google Chrome x64 62.0.3202.89
• uBlock Origin version: uBlock Origin v1.14.16