I've been working on compiling a bug report for shadow damage trinkets that are failing to fully benefit from mastery at times. Relogging, dying, and changing specs, a few times, will usually fix it. Not sure what's causing it. Only effects trinkets.
Glad to see I'm not just going crazy, doing 4.5M per cast two weeks ago across 10 fights to 3.5 last week. But later in the week for Normal back to 4.5.