As this issue only started recently for you, I would suggest looking into your router maybe being broken, or maybe a broken internet cable somewhere. Sadly hardware can break. (Note: Just because your internet works and is fast/reaches high speeds, does not mean your router can't be broken, or that your connection isn't unstable)

PS: It usually takes a few minutes for you to be able to log back in, as the server first has to detect you have lost your connection to it before finally logging you off.

Exactly the same happens to me too. The game simply closes completely when i am in specific dungeons, public dungeons, raids, group events. It happens if i am alone in a public dungeon and in group. It is not depending on being in a group, but it rather appears at specific places. Like for ex. the new public dungeon in eastern Solstice. If i run eastwards at some spot i just get disconnected. When i log back in and do some steps forward i disconnect again. I have to teleport out. If i run westwards all is fine. Same in raids. Some raids i can not do. In AA i get this constantly. Bastion Nymic before the end boss. Which is utterly frustrating cause by the time i am back on the group has disbanded and i did the run for nothing. I never crash outside of instances.
And i checked everything, the problem is not on my side. Something is wrong with those spots in the game. I repaired the game, i disabled addons, i set graphics all to the lowest (since the error is connected with a graphic error).
And just on a side note: the same happened years ago in Southern Elsweyr at a specific spot on the road. The game crashed every time i road over it. Which is now fixed.