Intermittent connection occurred on device which is not routed to IPSEC

[posemman]

We set-up policy base ipsec vpn on (HQ)fortigate 300c v5.2.15 and on (RO)Fortigate 60E v5.6.11 for MPLS backup.

The tunnel is up and traffic is flowing on both site. 

HQ local network: 172.27.14.0/24

Remote Local: 172.27.80.10/32 - This is client device, to only pass thru IPSEC 

Then the static route on HQ is:

172.27.0.0 255.255.0.0 to Internal Core Switch(MPLS connection)

             > AD of 20 Priority of 0

172.27.80.10 255.255.255.255 IPSEC to REMOTE

             > AD of 20 Priority of 1

0.0.0.0 going to (Public internet)

             > AD of 10 Priority of 0

--------------------------------------------------------------------------

Then the static route on RO is:

172.16.0.0/12 to router(MPLS connection)

            > AD of 10 Priority of 0

172.27.14.0/24 to IPSEC to HQ

            > AD of 10 Priority of 1

0.0.0.0 going to (Public internet)

            > AD of 5 Priority of 0

Ping and traceroute from RQ(172.27.80.10) to HQ - RESULT GOOD

1 <1 ms <1 ms <1 ms 172.27.80.254 2 * * * Request timed out. 3 10 ms 9 ms 11 ms 172.27.14.25

The issue is the other network device(172.27.1.2) pinging from RQ having intermittent connection(at least 10 packet drops) then it will up again and re occur again.

This network is not included in IPSec set-up, so I don't know why it is affected when IPSEC tunnel is up.

Do traceroute from RO going to 172.27.1.2 when intermittent occur:

1 <1 ms <1 ms <1 ms 172.27.80.254 - (FG gateway) 2 <1 ms <1 ms <1 ms 172.27.253.245 - (Router IP of RO) 3 7 ms 7 ms 8 ms 172.27.253.129 - (HQ MPLS Tunnel ip) 4 * * * Request timed out. 5 * * * Request timed out. 6 * * * Request timed out.