Not sure whether it factors in but switch chip features its own MAC address database which the kernel is unaware of. Moreover, the switch ship features its own VLANTable registers that work in conjunction with aforementioned MAC address database, supposedly some packets may not be reaching the kernel but remain within the switch fabric (purpose of the switch).
Now, however with lan3.1 there is a virtual (software) interface controlled by the kernel but not the switch (DSA) and that may (or may not) lead to a ARP Flux situation.
As far as I understand the better practice to manage VLAN tagging for DSA ports is via the bridge v command, e.g. as mentioned here