why "separate" and "union" function don´t not work in dplyr : I used the function "separate" and "union" to clean some data but they don´t seem to work

I´ve been trying to separate a column string into two columns using dplyr. The function is quite easy and don´t know why it does not work. 
The variable (column) I want to separate is “season” which contains values of “MAD_S1, KGA_S1” etc. (thousands of records, but the categories are 6, all separated by the “_S1”; raw data has been inspected and all follow the same syntax). Therefore, I applied

    separate(six_sites_spp, season, c("code_loc","season1"), sep = "_")

I have tried more explicit script such as: 

    separate(six_sites_spp, 
         col = "season",
         into = c("code_loc", "season1"),
         sep = "_")

but nothing either.

I have updated the dplyr versions, and try several things. If I use “union” instead to merge two columns it does not work either. I resolved this by using the classic “paste” function, but not for the splitting; I do however want to know why dplyr does not work (this is a great package and for some reason other commands are not working either).

Would anyone be able to provide feedback on this, please? Is it a possible “bug” or something within my system (windows10, HP envi), do I need another package simultaneously (I upload also tidyr in the same script)? any version mismatch (my R version 3.5.1 (2018-07-02). When I run the code it does something internally, as I see it runs the commands, but the output is the same dataframe (i.e. no new variables “code_loc”, “season1”

Many thanks in advance.

*there are no error messages