This StackOverflow question https://stackoverflow.com/q/61888967/2554330 motivated this report.

If the labels in scale_x_discrete are a factor, ggplot works fine. This is okay:

ggplot(diamonds, aes(cut)) + 
  geom_bar() + 
  scale_x_discrete("Cut", labels=factor(letters[1:5]))

However, ggplotly() fails:

ggplotly(
  ggplot(diamonds, aes(cut)) + 
  geom_bar() + 
  scale_x_discrete("Cut", labels=factor(letters[1:5]))
)
#> Error in nchar(axisObj$ticktext): 'nchar()' requires a character vector

Apparently an as.character() call is needed when ticktext is constructed.