The underlying problems are those of legacy software. People long gone from Linden Lab wrote this part of Second Life. The networking system predates the widespread use of middle boxes. (It also predates the invention of conflict-free replicated data types, which would have helped some higher level consistency problems.) The internal diagnostic tools are not very helpful. The problem manifests itself as errors in the presentation of a virtual world, far from the network layer. What looked like trouble at the higher levels turned to be, at least partially, trouble at the network layer.
The developer who has to fix this wrote "This made me look into this part of the protocol design and I wish I hadn't."
More than you ever wanted to know about this: [1] That discussion involves developers of four different clients, some of which talk to two different servers.
(All this, by the way, is part of why there are very few big, seamless, high-detail metaverses. Despite all the money spent during the brief metaverse boom, nobody actually shipped a good one. There are some hard technical problems seen nowhere else. Somehow I seem to end up in areas like that.)
[1] https://community.secondlife.com/forums/topic/503010-obscure...
Thank you for pointing that out. This thread alone is bound to become a meme.