as you can see in attached image, Toggle text are invisible but i can see it if open page source, it look like something with CSS. the other image is normal view without Collapsed Topics selected.
In M3.3 and with the Boost theme, section titles are black, but in the screen shot they are blue. Therefore you have some custom CSS / SASS that is causing the issue.
Screenshot of the Clean theme please. Plus as the section titles are 'blue' in the standard topics format then something is changing that from the default. Therefore what contributed plugins do you have installed?
I installed from git without editing any css or php and have not installed any plugin besides yours. Screenshot of Clean attached.
Still cannot replicate.