You may be already aware of this issue via other support tickets, so feel free to shoot out a generic update to me if you're already working on a fix.
We updated two sites from Yootheme Pro 2.3.27 (which was working fine) to 2.3.30. After the update, when clicking the "Yootheme Builder" button when editing an article, it now shows a 404 error within the Yootheme Builder.
However, if you immediately click to another navigation item (still within the YT Pro builder), the builder comes back and is usable. For whatever reason, the Yootheme Builder editor button appears to be going to an incorrect editing URL when used from the frontend of the website. You can see a quick video of this behavior here https://we.tl/t-xxxx
A couple nuances that may aid your troubleshooting:
1) The builder starts working again if we DISABLE sh404sef (even if we leave on url rewriting and sef URLs enabled in Joomla config
2) Even with sh404sef enabled, editing the article via YooTheme Builder works correctly in the BACKEND of joomla. But front-editing exhibits the 404.
3) We believe this is a conflict between Yootheme Pro and sh404sef introduced in version 2.3.28 actually (see their change log here https://yootheme.com/support/yootheme-pro/changelog). Note that they updated generating routes (Joomla).
4) I believe you troubleshot a similar issue in the past https://yootheme.com/support/question/126316
The site we would like you troubleshoot is https://www.xxxx.com/
Username: xxxx
Password: xxxx
Admin URL: https://www.xxxx.com/administrator/
Note that I mentioned we upgraded this on a second site - development site, which exhibits similar 404 behavior, so we have confirmed the conflict.
Let me know if you have any questinos