Including outgoing link tab looses splitter function

What I’m trying to do

I have a file open (“HASE Homburger ADHS-Skalen für Erwachsene”), the graph view, and the right tab with the calendar. Everything works fine. I can use the splitter to rearrange the space of the tabs. But when I add the outgoing link tab there is no more splitter line to arrange space between the file tab, the outgoing link tab and the graph view tab.
Is there a way to reactivate the splitter function?
The splitter function between graph view and the right tab is still working.

Things I have tried

I reopened Qbsidian, but the problem persists.
I restarted PopOS but no difference.

“split”
“splitter”

The problem is solved! The splitter work fine again!