Thanks! Here is a rather contrived reprex that demonstrates the problem. (I had the impression that the ... would forward the additional named arguments, but this does not seem to be the case.)
library(ggplot2)
#> Registered S3 methods overwritten by 'ggplot2':
#> method from
#> [.quosures rlang
#> c.quosures rlang
#> print.quosures rlang
ggplot(mpg, aes(factor(cyl), hwy)) +
stat_summary(fun.y = mean, geom = "col") +
stat_summary(aes(label = round(stat(y))),
fun.y = mean, geom = "text", colour = "yellow",
nudge_x = -0.2)
#> Warning: Ignoring unknown parameters: nudge_x

ggplot(mpg, aes(factor(cyl), hwy)) +
geom_col(fun.y = mean, stat = "summary") +
geom_text(aes(label = round(stat(y))),
fun.y = mean, stat = "summary", colour = "yellow",
nudge_x = -0.2)
#> Warning: Ignoring unknown parameters: fun.y, stat

Created on 2019-05-13 by the reprex package (v0.2.1)