Yes - it's a bug in old unmaintained linux kernels. My solution was to change the router for something more modern. The kernel version used in rt-ax88u for instance does not have this bug. Note though that for this router, asus merlin does not support snmp in the base installation, but you can install the mini-snmpd package via entware. I've been using this setup for a while and it works great
Thanks for the answer. Seems a bit confusing to figure out which routers have a "modern" kernel plus which have an older "unmaintained" kernel. Plus the rt-ax88u seems pretty pricey, any suggestions on a cheaper router that has the more modern kernel and would therefore support SNMP stats correctly ?