Hello,
As per the above logs i believe you are seeing the packets getting dropped on the ISG side.
As per the logs please check the route and policy on the ISG side for the traffic from LAN on the ISG side to the SRX and see if it is correctly pointing for it to go over the VPN tunnel or not.
Thanks,
Pulkit Bhandari
Please mark my response as Solution Accepted if it Helps, Kudos are Appreciated too. 