Is there a key map conflict in my Vim?

I use the two command below to map my `j` and `k`, the purpose of these command is that when the current line is too long, it will be wrapped in vim window, and you don't want to jump it when you press j or k. So ~
nnoremap <expr> j v:count == 0 ? 'gj' : 'j'
nnoremap <expr> k v:count == 0 ? 'gk' : 'k'

It doesn't work when I enter vim, but it worked when I run the command

`source $MYVIMRC`

I check my vimrc file no key map conflict in it. It means that my plugin get some duplicated key map ?

How to fix it ? I use gvim 8 on windows


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