@elorimer - I did hear back from the vnStat application owner (Teemu) and got pretty much the same answer "saw it once on a Raspberry Pi, haven't been able to reproduce it" and "no other reports", so it's obviously something specific to your setup.
He did ask if we are running a vnStat daemon (we're not) to see if there's something logged, and suggested
strace
, but since I have no way of reproducing the situation, it'd need to be done from your machine.
Out of curiosity, which version of vnStat are you running (
vnstat --version
) - I'm assuming it's 2.xx.
I guess there's a couple of options: 1) the aforementioned nuclear reset/reconfiguration or 2) creating a script that periodically runs the command
/tmp/mnt/<<usb drive>>/entware/etc/init.d/S33vnstat stop && /tmp/mnt/<<usb drive>>/entware/etc/init.d/S33vnstat start
to restart the underlying application. Not pretty but it might beat the reset.