TYPO3 Core

Hello, actually i'm trying to update a Typo3 6.2 website to Typo3 7.6. (actually Typo3 7.6.19)

While testing the localization with IRRE CE I found a bug. This bug only appears with Typo3 standard elements.
The backend view from the Plugin

If I hit the localize button, it seems nothing happens.
But in real, the CE gets translated and a correct n:m connection is set.
Just the ajax don't change the frontend view of the backend.
If I hit now the save button, it will save the actually view & delete the n:m connection...
If I hit the close button and enter the CE again, I will see the localized CE and everything is fine.

I debugged a bit of the core with the help of this response information.
There is a scriptCall¹ Ext.onReady.... which makes problems.
That one calls a JS function with TypeError: Cannot read property 'dom' of null. !JS Error.png!

I'm catching that error and returning true to skip that. (hackJs.png).
And the result is kind of nice, CE gets localized but the categories tab is empty.