Since the sync for week 23/24 I started having issues with icon fallback.
My current icon theme is complicated: the theme itself basically only has an handful of apps, then it inherits from other themes which provide more apps and then from papirus which provides basically all the monochrome icons for buttons and panels.
Since that update, it looks like only the first inherited theme is taken into account, while the others are ignored.
For example, let's say I am using Theme1, which has
Inherits=Theme2,Theme3,Papirus
inside index.theme.
Theme2 provides the icon for the color picker, while Theme1 and Theme3 do not.

If instead I swap the inherit field as
Inherits=Theme3,Theme2,Papirus
the icon, since it's not provided by either Theme1 or Theme3, should be still taken from Theme2.
Instead, it is taken from what looks like hicolor.

@brent I remember you having a similar issue at the time, could you verify if it is related to fallback in your case too?
For the Budgie experts, does anyone know what code handles the icon fallback?
P.S. Arch is seeing something similar too https://bbs.archlinux.org/viewtopic.php?id=296932