No button visible (Avada Theme Builder and ACF Editor)

Avada Theme Builder is active on my website, as is ACF Pro, whose WYSIWYG editors I use, and no icon is visible. When I move the mouse over the area where the button is, an empty frame is visible and the button itself works.

Any idea how I can make the icon visible?

Have read here that there are partial problems with other themes/plugins.

But I can’t disable ATB or ACF.