There was a bug in the computation of permissions for relations in the context of displaying reledit form. It has been fixed in version 3.32 of CubicWeb.
The method _should_edit_relation who chooses if the reledit form must or not be displayed. This is computed through the method cubicweb.schema.CubicWebRelationSchema.has_perm, which will (among others things) try to satisfy all RQL expressions for permissions.
This expression will generate a RQL request like AnyO,UWHEREUhas_update_permissionO,Oeid%(o)s,Ueid%(u)s which will not be satisfied, because the eid of the object wonât be given by reledit.
In consequence, we have to find an other way to check permissions for reledit.