TypeError on frontend when narrowing browser in multi column mode

[zunda]

Expected behaviour

Browser shows the single expected column after narrowing the browser window in multi column mode.

Actual behaviour

Browser shows the sad elephant. Browser console shows TypeError in components/column_header.js because document.getElementById('tabs-bar__portal') returns null.

ThibG reported this may also happen for the ColumnBackButton component.

Steps to reproduce the problem

Enable multi column mode, navigate to HTL or LTL, than narrow the browser window.

Specifications

I noticed the problem on a server running on master at f96f45e around August 3rd, 2019. The problem is seen at least on Firefox on macOS, Firefox on Linux, and Chromium on Linux.

It turned out my proposal for a fix on #11605 is premature. I'd like to move the conversation here and seek for a better solution from experts.