So recently I tested my router for packet loss and its kind of weird. Every tests were done with 5000 packets.
Every tests were done on a computer behind the network. So I used win mtr on my router to continuously monitor the amount of packet loss. I also used pingplotter with TCP packets, just in case ICMP would be dropped by my router for some unknown reasons.
5000 on wired = 2% packet loss
5000 on 2.4ghz = 0.2% packet loss (i blame the 30 APs around me, but its fine)
5000 on 5ghz = 0% packet loss
However, the packet loss on the wired connection only happens when the WAN cable is plugged in. If I unplug it, everything is fine. No packet loss while running LAN tests. After the LAN tests, I decided to test it over WAN (testing servers on the internet) and I got the same packet loss.
I switched to stock firmware. Tested on LAN side (192.168.1.1) while the WAN cable is plugged in, I was able to get to 5000 packets without any losses.
It feels like there is an issue with Shibby that screws up the LAN ports when the WAN cable is plugged in, which does not happen when its unplugged.
I have no idea if it happens on older versions but I am using the latest one.