Good Evening,
I installed Openwrt recently on the EA6350v3, and encountered this same issue.
The WAN and LAN ports are handled by the same ethernet controller on this device.
If you pump too much data through the controller it locks up.
I was only able to trigger this with a hardwired device, wifi doesn't appear to run enough bandwidth to trigger the bug.
It seems to be similar to the issue plaguing rk3328/rk3399 ethernet controllers, where heavy load causes the ethernet controller to lock up.
On the rockchips, if you send too much data through the controller with tx coe offloading enabled, the buffers get overloaded and the controller crashes.
Unfortunately disabling offloading on the ea6350 only raises the threshold for the bug to trigger.
I was unable to fully diagnose the issue, before being forced to return to stock firmware.
This seems related to the issues people have with certain websites not working correctly, which can be mitigated by lowering the MTU.
I found references of a new ethernet driver being developed by @blogic, but I cannot find the actual driver.
Mainline linux does not have a driver for this ethernet controller.