Parallel estimation of multiple nonparametric models using np and snowfall

Question

I am trying to estimate multiple nonparametric models using snowfall. So far I had no problems, but now I run into a problem that I feel unable to resolve.

In the MWE below we simply estimate only one model on one node. In my application the structure is the same. When I try to plot the model results or use another function from the np package (like npsigtest()), I get the error

Error in is.data.frame(data) : ..1 used in an incorrect context, no ... to look in

Has anyone an idea what causes the problem? I am open to another approach concerning parallel estimation of several models.

MRE:

library(np)
library(snowfall)

df     <- data.frame(Y = runif(100, 0, 10), X = rnorm(100))
models <- list(as.formula(Y ~ X))

sfInit(parallel = T, cpus = length(models))
sfExport("models")
sfExport("df")
sfLibrary(snowfall)
sfLibrary(np)
lcls <- sfLapply(models, fun = npregbw, data = df, regtype = "lc")
sfStop()

plot(lcls[[1]])