Hmm. I copied all data to new project as sandbox and it is working.
I need to investigate this task in dev tools. How Can I block TaskEditor to always visible? If I click on another window TaskEditor is closing.
The problem is with flexbox. For some unknown reason width is calculating very strange.
But I think bug is still exist, because my CSS in app didn't affect to task editor.
First a tip in Chrome DevTools. You do not need to block anything to keep task editor visible, Chrome has a setting to keep focus on the page when you access dev tools. It is called "Emulate a focused page" and you can find it on the "Rendering" tab (under "More tools").
Secondly, the issue was fixed by fixing the locales. Perhaps you are using an old locale?