FWIW, that system is Solaris 10
SunOS c3pg 5.10 Generic_141414-10 sun4us sparc FJSV,GPUZC-M
I'm also seeing this problem on a 4.1.2 agent on Solaris 9. I didn't run the SIGAR test on that system, but I checked it in HQ and it is missing all of its disk stats (disk reads/min, disk writes/min, and disk service time), though it does have disk usage stats. But I noticed "df" and "du" in SIGAR worked, so that makes sense.
I'm not sure how to further debug, would love any ideas 🙂