I am not sure if this is a known issue or if I'm the first person to report it, so I'm only posting it in here for now without having sent a bug report yet. Since one of the latest updates/hotfixes, the dialogue boxes of NPCs keep closing while I'm still in the middle of reading the text which can get really annoying, especially for dialogues with a lot of pages to click through.
After some testing with a friend, we found out that the reason for the dialogue box to close is a player character running into and then out of the radius in which I could normally keep my dialogue opened without having it auto-closed for running away. It does not seem to have any effect at all if that player character has the dialogue opened as well and then closes it. It does not even have an effect if the other character is in my party or not, so random strangers running past me in public areas keep closing my dialogues. My friend and I repeated our tests several times to make sure this problem is reproducible and the same effect happened every time. As soon as one of us ran out of the radius in which the dialogue box can be kept open, no matter if the moving person had the dialogue opened as well or not, the dialogue closed for the other (not moving) person.
Steps to reproduce:
1. Find another person to test this with you
2. Go open a random dialogue box with a random NPC (a questgiver or whatever)
3. Stay where you are with the dialogue opened
4. Have the other person stand close to you, and then have them run away from the point where you are standing
5. Your dialogue box will be auto-closed as soon as the other person has surpassed a certain distance
(no matter if they had the dialogue opened, too, or if they were just passing by and also no matter if they are in your party or not)
If for some reason, this is only happening on my friend's notebook and on my computer and other people can't reproduce it, that would be good to know, too. And if the server is of any relevance, it happened on Wayfinder. If any additional information is needed, I'll gladly provide it, and of course I can also write a real bug report if this is not a known issue yet.