Iexo Bethune
After spending a certain amount of time in a region, the player enters a state where they can continue to remain in the region, interact with things in the region, and chat in local or IM indefinitely, but when they try to teleport out, cross a border, or certain other actions, it will fail and they will be logged out.
This is a relatively old issue, and having spoken with Monty Linden about it, it appears (at least as I understood it) that the player becomes soft-disconnected from the grid, without disconnecting from the region they're in.
What's different now (within the last month or two) is that the amount of time needed to be spent in the region to trigger this has vastly shrunk, from several hours, to as little as 5-10 minutes. As a result, more and more people are experiencing teleport and crossing failures and random logouts recently.
Edit: This state can usually be identified early by alt-camming on something far away. While the surrounding regions already loaded will remain loaded, all regions beyond them will never load, even when alt-camming on something that puts them well within the view range.