Hmm, I think I may have an issue as I when I did the DietPi update it wasn’t able to update JF. I deleted JF and tried to reinstall, but got a the same error message as i did during the DietPi update. Not even sure if JF is installed 
I got this when I pasted the code:
root@DietPi:~# G_CONFIG_INJECT 'JELLYFIN_LOG_DIR=' 'JELLYFIN_LOG_DIR=/mnt/dietpi_userdata/jellyfin/log' /etc/default/jellyfin
G_CONFIG_INJECT 'TMPDIR=' 'TMPDIR="$JELLYFIN_CACHE_DIR/temp"' /etc/default/jellyfin
[ OK ] G_CONFIG_INJECT | Setting in /etc/default/jellyfin adjusted: JELLYFIN_LOG_DIR=/mnt/dietpi_userdata/jellyfin/log
[ OK ] G_CONFIG_INJECT | Comment in /etc/default/jellyfin converted to setting: TMPDIR="$JELLYFIN_CACHE_DIR/temp"
but JF still not working