I recently upgraded from 2.7.15 to 2.7.16 and encountered a bug that no JCE editori is being displayed in second tab of custom fields.
After downgrading to 2.7.15 things get back to normal.

Images:
1. Custom fields configuration
2-3. Normal state of things in "Autorius" and "Šaltinis" tabs.
4. After upgrade to 2.7.16 no JCE editor on "Šaltinis" tab. Pressing on/off button in top left launches some process and spinning wheel is shown and if I would press "Save" button of the article, entire text of the article is gone.

Hi,
I have a similar issue using the component "seblod" to display multiple WYSIWYG-Editor fields in backend. Some fields work, some not. Downgrading to JCE 2.7.15 solved the issue for me, too.
Best regards
Sven

I've spotted the same issue in 2.7.17, Downgrading to 2.7.15 fixed this.

To me it looks like that using more than one editor on a page is causing issues with initialising all editors from the second one

Hi.
With RC6 this problem is solved.