Changed the firewall as per your suggestion:
/ip firewall filter
add action=accept chain=input comment="defconf: accept established,related" \
connection-state=established,related
add action=drop chain=input comment="defconf: drop invalid" connection-state=\
invalid
add action=accept chain=input comment="defconf: accept ICMP" protocol=icmp
add action=accept chain=input comment="Allow ADMIN to Router" \
in-interface-list=LAN src-address-list=allowed_to_router
add action=accept chain=input in-interface-list=LAN port=53 protocol=tcp
add action=accept chain=input in-interface-list=LAN port=53 protocol=udp
add action=drop chain=input
add action=accept chain=forward comment="defconf: accept in ipsec policy" \
ipsec-policy=in,ipsec
add action=accept chain=forward comment="defconf: accept out ipsec policy" \
ipsec-policy=out,ipsec
add action=fasttrack-connection chain=forward comment="defconf: fasttrack" \
connection-state=established,related
add action=accept chain=forward comment="defconf: accept established,related" \
connection-state=established,related
add action=drop chain=forward comment="defconf: drop invalid" \
connection-state=invalid
add action=drop chain=forward comment="Drop in from WAN not DSTNAT" \
connection-nat-state=!dstnat in-interface-list=WAN
add action=drop chain=forward dst-port=53 in-interface-list=WAN protocol=tcp
add action=drop chain=forward dst-port=53 in-interface-list=WAN protocol=udp
Still, subnet is not pingable , neither new subnet device shows in the dhcp-server lease export. Though, can be seen in the winbox.