Theme config not being loaded when put in a separate file

[rbhanot4739]

Hello,

Thank you for making this amazing theme. I am having slight bit of issue that when I move my theme config to a separate file, the config is not applied. So here is what I have in my tmux.conf and the value of USER_THEME is set to gruvbox.

if-shell -b 'test -n "$USER_THEME"' "source-file ${HOME}/scripts/tmux/${USER_THEME}.tmux"

And here are contents of ${HOME}/scripts/tmux/${USER_THEME}.tmux

set -g @tmux-gruvbox 'dark256'
set -g @tmux-gruvbox-statusbar-alpha 'true'
set -g @tmux-gruvbox-left-status-a '#h'
set -g @tmux-gruvbox-right-status-z '#[bold]#S #{tmux_mode_indicator}'

However if change my tmux.conf to below the theme is loaded but with default config but none of the options from ${HOME}/scripts/tmux/${USER_THEME}.tmux are applied. Strangely, if I reload the tmux same config in a running tmux session then the custom options from the file are applied.

set -g @plugin 'egel/tmux-gruvbox'
if-shell -b 'test -n "$USER_THEME"' "source-file ${HOME}/scripts/tmux/${USER_THEME}.tmux"

I am not sure if there is something I am missing in my config (obviously don't know the internal details tmux theme loading works etc), but I am not able to figure this out. It could be very much possible that this issue isn't directly related to this theme so apologies in advance for that.