The CPU barely moves from 1% and the load average is always at least 0.50 (without activating the experimental offloading firewall)
and changing the subject.
Without activating experimental offloading firewall, the router seems stable, with this and HW NAT quite unstable, it lasts at most 3 days and it hangs
"INFO: rcu_sched detected stalls on CPUs / tasks:"
appears in dmesg but I guess that's why it says that it is still experimental 