Created attachment 730957 [details]
mesa_err.log
I was able to find an important clue, while running Xonotic using the following
environment variables:
MESA_DEBUG=1
MESA_LOG_FILE=/foo/bar/mesa_err.log
A log is generated and readable after restarting the machine. It only contains
one line, but that looks like it might address the cause:
Mesa: User error: GL_INVALID_OPERATION in glGetQueryObjectiv(out of bounds)