Thunar's search-in-process spinner (spinning circle animation) is very dim with Zoren dark themes. So dim, in fact, you might have missed it - look directly above the Search icon. To fix this, add the following to ~/.config/gtk-3.0 file:
/* lighten spinner (search in-process) */
.thunar spinner { color: #ffffff; }
.thunar spinner:checked:disabled { opacity: 1; }