Cycle detection does not work with groups
In a setup like this
flowchart TD
B --> C
C --> A
subgraph group
A -.-> B
end
(where the dotted line indicates a weak connection), we run into a deadlock. This is because C waits for the conclusion of the calculation in the group, but the calculation in the group depends on the output from C.
This should be detected before the simulation is started. The current algorithm (check that the graph is non-cyclic after removal of time-shifted and weak connections) does not work in the presence of groups.