The last several batches of icing I've made have been clumpy. Tiny little clumps perfectly sized for clogging tips. At first I thought it was brand (I had bought a couple bags from a different store than usual) but then I went back to my regular brand and same issue. I've never had this issue before.
The only other possible variable is the meringue powder. I'm using the same brand, but purchased my most recent powder in bulk. But it's fresher and less clumpy than the older stuff I was using, and I run it through a sieve anyway just in case.
I haven't sifted powdered sugar for YEARS (haven't had a need to!) but that's my next step.
It's a powdered sugar conspiracy obviously.