This is not about “OCE ping”. I am very used to that as well as its ups and downs.
I have several OCE friends I play with very regularly with zero issues outside of the normal increase to latency, but the last ~24hours or so the game has been unplayable in Mythic+ especially when OCE is hosting the group. It is not 100% constant but it is quite often. The worst from last night was when we attempted to do Underrot on OCE - two OCE players (both Barthilas if it matters) and 3 US players. All three of us from the US were lagging out constantly while the OCE players were totally fine. Before we decided to give up on the key the longest I went without lagging out was probably ~80 seconds.
It was better once we reformed the group on NA, but for instance this morning after waking up… we had another 3 US/2 OCE group (both Frostmourne this time) and we had the same issue in reverse. One of the OCE players would not lag out completely but had constant 1200+ latency while the other OCE player disconnected repeatedly over the course of about 45 minutes. I don’t know the specifics of WoW’s instance servers but the worst this morning was also in Underrot.
*PM Update *
Had this as a draft that I did not submit, but issue still occurring. Attempted to assist OCE players with a Neltharion’s Lair a short while ago but while inside the dungeon applying my buffs I again lagged out but luckily before the key was started this time. Group was formed on Barthilas.