Found it.

Signed-off-by: Dan Schaper <dan.schaper@pi-hole.net>

advanced/Templates/pihole-FTL.service

@@ -23,7 +23,7 @@ start() {
     mkdir -pm 0755 /run/pihole
     [ ! -f /run/pihole-FTL.pid ] && install -m 644 -o pihole -g pihole /dev/null /run/pihole-FTL.pid
     [ ! -f /run/pihole-FTL.port ] && install -m 644 -o pihole -g pihole /dev/null /run/pihole-FTL.port
-    [ ! -f /var/log/pihole-FTL.log ] && install -m 644 -o pihole -g pihole /dev/null /var/log/pihole.log
+    [ ! -f /var/log/pihole-FTL.log ] && install -m 644 -o pihole -g pihole /dev/null /var/log/pihole-FTL.log
     [ ! -f /var/log/pihole.log ] && install -m 644 -o pihole -g pihole /dev/null /var/log/pihole.log
     [ ! -f /etc/pihole/dhcp.leases ] && install -m 644 -o pihole -g pihole /dev/null /etc/pihole/dhcp.leases
     # Ensure that permissions are set so that pihole-FTL can edit all necessary files