High CPU usage (50%~70%) when downloading with multiwan config

[heliocsa]

• Pfsense version 2.4.3
• Processor: AMD FX-4300 with 8GB RAM
• Packages installed: squid, squidguard, pfBlockerNG-devel 2.2.1 running with DNS Resolver configured and DNSBL/Feeds
• 4 fisic network cards + 2 VLans
• DualWan config to Failover (Wan1 default 100MB at tier1 and Wan2 with 20MB at tier2)

When I trigger a big HTTP download (300MB+), with the dualwan config activated, my CPU usage spikes up to 50%~70%, sometimes get to 100%, which is weird I guess (if it gets to 100% the server just freeze). When it's happening the traffic "in" just get to top of usage only on the second wan. But when I disconnect the second wan (disconnect the network cable from the network card) the CPU usage backs to normal. I have tried everything to make sure it's not an issue on the hardware or something else. If I make a reset of states it's back to normal for some hours. If I deactivate the dualwan setup everything run normal and CPU usage do not pass the 13%~16% for days on.

Someone have any solution?