I have noticed that server processing is making changes to the avatar performance rankings without any indication as to where the problems could be lying within the avatar. This can cause a particular problem where an avatar creator has gone through the effort of optimising the avatar to at least poor or better as indicated by the VRChat SDK, however, in game it goes back to being rated as very poor.
Take this example. I have an avatar that is Very Poor to begin with, but, the Bounding box rating is Good according to the SDK readout. Because this avatar has VRCFury components on the avatar, I needed to rule out that it is VRCFury. I proceeded to create a local build and test version for the avatar. When loading the build and test version on VRChat, the bounding box also is good according the VRChat stats. I then upload it to the VRChat servers and when I load the uploaded version, the bounding box goes from Good to Very Poor with no indication of where that detail is coming from. This therefore rules out VRCFury on the avatar and likely indicates that the server processing is doing something to the ratings without prior knowledge.
For VRChat devs, here is the avatar ID that I am talking about (private avatar): avtr_77276e80-fdcc-4f0c-9f3d-2613f9bf28a1