This latter appears to be the problem:
Intel Extreme graphics are not compatible with Second Life. It may be possible for certain configurations of hardware and software to successfully run Second Life while using Intel Extreme graphics; however, these configurations are not inherently stable, and small changes to Second Life (as Linden Lab provides better graphical features and support for compatible graphics cards) may leave these systems once again unable to use Second Life due to incompatibility.That's according to the SL wiki
Oh dear. Obviously all these years I've been right not to have Intel Inside lmao.
There's a similar problem, ongoing for 2 years, about avs rendering parts of the environment or IM window, and the most recent reply from Esmee Linden:
This is fundamentally tied to our rendering architecture. Fixing it requires redoing big chunks of our texture pipeline. Although it's a bug, we're not currently working on it. However, we might at some point in the future.Fine. Just add more stupid features instead. From the JIRA https://jira.secondlife.com/browse/VWR-3282