Hello E.,
Here is a first workaround with erasing 'style=wedged', as:
@startuml
digraph g {
label="Floresta de domínios"
labelloc=b
nodesep=1
forcelabels=true
graph [labelloc=b]
node [label="" shape=triangle style=filled width=2. height=1.5 fixedsize=true]
subgraph cluster_1 {
label="Árvore de domínio"
a [label="contoso.com"]
b [label="usa.contoso.com"]
c [style=invis]
}
subgraph cluster_2 {
label="Árvore de domínio"
d [label="fabrikam.com"]
}
concentrate=true
a -> b
b -> a
a -> c [style=invis]
a -> d [constraint=false dir=both label="Relação de confiança\nTransitiva Bidirecional"]
}
@enduml

Regards,
Th.