When I use Fast Downward (version FDSS 2014), I notice that the planner cannot deal 
with more than 3 quantifiers defined in the domain. For example, 
(exists (?j1 ?j2 ?j3 - junction)
  (connect ?j1 ?j2)
  (connect ?j2 ?j3)
)
The planner will be stuck in the processing step.

We have discussed this further by email, and it looks like the problem is with
the negation of axioms. This is already covered by issue450, so I am closing
this one, but adding the PDDL example that triggered the problem for this issue
to issue450.

In principle, this construction is no problem, but if there is a large number of
quantified variables and parameters and a large number of objects, eventually
the combinatorial explosion will catch up with you. There is no good solution
for this in general, but we can have a look if something can be done in your
specific use case. Can you attach a domain file and problem file that showcase
the problem?

Please note also that FDSS 2014 is now five years old. I would recommend trying
it out with a more recent version of Fast Downward, although it is likely that
in your case it won't make much difference, as there have only been few changes
to the translator step since then.