Why do some canard aircraft have dihedral on their canards? For instance, Rutan's Solitaire and Steve Wright's Stagger-EZ. What are the benefits of having a dihedral on the canard?
It seems like the canard dihedral increases yaw instability, and requires a bigger vertical stabilizing surface. Yet there are flying GA airplanes and sailplanes using canards with dihedral, and they've surely thought of this. What's the reason for that?
(My opinion-based hypothesis is that it's about very stalled AoA behavior, where canard dihedral may naturally slow down some flat spin, and help with recovering from it; still, I cannot find any references about this, and it may also be a very wrong statement as long as it's opinion-based.)

(Rutan's Solitaire)

(Wright's Stagger-EZ)

(Saab Gripen)
Edit:
Gripen also has dihedral on canard surface, however since those are full moving surfaces with high sweep angle, depending on the angle of attack, those surface viewed from the front, display either dihedral, no dihedral, or anhedral (if very positive canard AoA)
If it is a canard, the assumption of a well thought out design is doubtful. Yes, dihedral will add to directional instability and require a bigger tail, but at least in case of the glider the vertical is sized for countering adverse yaw, so the bit of canard instability is easily compensated.

My direct response would be: To lift the core of the canard wake above the wing. But from looking at the Solitaire I wonder whether that is really true. At least on the Stagger EZ you can see that the designer tried his best to separate canard and main wing vertically.

Regarding flat spins: The spin axis normally runs through the forward fuselage, so there is not much horizontal airspeed at the position of the canard. The tail will help to dampen the yawing moment much more. A bit of canard dihedral will not make a difference.

But maybe wing dihedral was found to be lacking during flight test and changing dihedral on the canard seemed to be an easier fix? That would be my best guess, at least for the Solitaire.