Missing data files in R

Question

I use R bind to combine multiple files into 1 df. When I close R, about 6 of those files disappear from my environment. The code is still saved with those file names in the script where I type the codes, but I have to reimport those files every time I close and reopen R.

Here is my code. It is the first part of a vary long pipe

master_df<-rbind(A_2,Ft_A_3, A_4,A_5,A_6
                 B_1,B_2,B_3,B_4, B_5,B_6,
                 C_2, C_3,C_4,C_5,C_6, 
                D_3,D_4,D_5,D_6,
                E_2,E_3,E_4,E_5,E_6,
                 F_2,F_3,F_4,F_5,
                G_2,G_3,G_4,G_5,G_6,
                 H_1,H_2,H_3,H_4,H_5,
                 I_1) %>%

This is the message that is displayed when I rerun the rbind code:

Error in rbind(deparse.level, ...) : object 'A_6' not found

It will then reprint the same code with the next missing object once I reimport that previous file.

I have saved all of my scripts, work space, and history. I do not change where these files are located either on my computer