I’m raiding on NA Defias Pillager and I’m from EU. The last 2 days while in a raid group, and ONLY when in a raid group, the EU players in the raid (from 3 different countries) have all started lagging and disconnecting at the same time - once during AQ20 and once in Naxx - while the NA players has had no issues. There were 4 EU players who all lost connection and started lagging while the 5th and last EU player in raid had no issues as he was using a VPN connected to the US and not Europe.
Has anyone else experienced this the last couple of days, and are there any known solutions? All our internet connections were fine and we communicated clearly through discord, so it was just the game itself we lost connection from, and it’s ONLY happening in a raid group - not while not in a party or in party groups of 5.
Same thing keeps happening to me and my friend, we are both in Europe, playing on an American server. We have started getting high latency and disconnects every single day for a week now (more or less), while in party (i think my friend got it in a raid as well, a week ago). The “bots” from tech support have no clue. Help, anyone? 
Everyone I know in EU playing on NA is having same issue…get random lag spikes or DCs during the day, then at night almost on the nose between 830-840PM bam game is unplayable. I tried sending in a ticket but kept getting bad automated responses from Blizzard!
You can try a vpn, see if that helps. If it does it might help to know what isp, and what countries are affected.
Maybe some self help things about optimizing your connection? Unfortunately there is very little outside of this that blizzard can provide.
The Issue I have seen its affecting those with VPN’s I know a few using them, as for what countries, Norway, Sweden, Germany,Poland,Belgium,Denmark to name a few that I know just right off the cuff. So VPN does not seem to be the issue. Its been over the last two weeks.
With all the DDoS attacks there has not been a release about this being an issue. Again not sure how many people in Europe play on NA, but I know im not the only one complaining and messaging blizz about it.