HI Dimi,
The flow trace shows traffic flow "10.0.110.11/1201->x.x.x.x/1194;17" is entering on "reth2.110" and leaving out on "pp0.3".
Please check the output of "show route x.x.x.x detail" during working and non-working state to confirm if the route changes and if so why ?
SRX is not dropping the packet but re-routing it through pp0.3 interface. If you believe this should not happen then please check the route table during non-working state to find out the reason for change in interface.
Thanks,
Kinshuk