Ok, I think I got it.
This afternoon, I changed some wifi options (disabled the 5GHz network, keeping on just the b+g+n).
As soon as I applied the mods, the network options were reloaded and qosmon was terminated. It never got back up, anyway.
So I think it's been happening any time I change some networking options.
Would it be possible? Unfortunately I do not have the logs, but the qosmon status file on /tmp was last updated exactly when I applied the network mods.