I had a lag spike situation on a steamos machine playing a game called shape of dreams when using wifi but not ethernet, and it wanted a network card driver update. Kind of a shot in the dark but you might try it.
I'm reading that there's a network stats API that addons can use https://warcraft.wiki.gg/wiki/API:GetNetStats
Maybe there's a network performance monitor addon you could find, but I don't have suggestions there.

