Having the same issue. Ping completely normal, until i get 4k-5k spikes. Sometimes the client looses connection. My internet connection is fine, we even got a new router and everything a week ago (First few days afterwards everything was normal, until the random lag spikes appeared). Seems to be a game/ server related issue.. which is really annoying, cause there seems to be no real cause for me for these spikes and lags and i can't do any bigger events or raids out of fear i will be "unlucky" again. Hopefully you can fix this 😕 I can't rly play like this atm.
I also updated my grafic driver, cause before i had random crashes cause of that i guess.