maybe someone is broadcasting/flooding your network?
Also please upgrade your RouterOS to a newer RouterOS version.
So what can I do? use ip>firewall?
Check the torch what is it and make drop rule. But you should drop everything in general and allow only wanted traffic.
In multi wan through vlan+bridge+pppoe, the vlan’ rx traffic are higher.
but in single wan, is not appear.
Is the vlan’s problem or the vlan swith’s setting problem?