Adding labels to geom_edge_parallel causes some edges to collapse onto each other.

(Perhaps labels and parallel edges are not a great idea, but it could be nice to display two edges in opposing directions, instead of using arcs.)

Reprex:

library(ggraph)
library(tidygraph)

gr <- create_notable('bull') %>%
  convert(to_directed) %>%
  bind_edges(data.frame(from = c(1, 2, 2, 3), to = c(2, 1, 3, 2))) %E>%
  mutate(class = sample(letters[1:3], 9, TRUE)) %N>%
  mutate(class = sample(c('x', 'y'), 5, TRUE))

ggraph(gr, 'stress') +
  geom_edge_parallel()

ggraph(gr, 'stress') +
  geom_edge_parallel(
    aes(label = 1), 
    angle_calc = 'along', label_dodge = grid::unit(20, 'points')
  )

The first works fine:

But for the second (with labels), there are edges that are now on top of each other again.

(P.S.: You can also see that label_dodge appears to be calculated from middle of the group of edges, and not each individual edge, but this may be difficult to fix.)