Kind of an obscure issue but definitely an issue:

library(future.apply)

plan(sequential)
future_lapply(
  X = 1, 
  FUN = function(x) {y}, 
  future.globals = list(y = 4)
)
#> Error in ...future.FUN(...future.X_jj, ...): object 'y' not found

z <- 1
future_lapply(
  X = 1, 
  FUN = function(x) {y}, 
  future.globals = list(y = z)
)
#> Error in ...future.FUN(...future.X_jj, ...): object 'y' not found

Created on 2018-05-09 by the reprex package (v0.2.0).

Interestingly, the y value is recognized as a global, and makes it into the environment that the expression is evaluated in. You can see this by debugging and making your way to this line of run.UniprocessFuture(). Not sure why it can't be seen inside the lapply() after that