Help!!! I'm getting several small cracks (1-2" long, hairline cracks) in my smooth, crusted buttercream.

Same buttercream recipe (Sugarshack) I've been using for over a year. Never used to have a problem with the smoothed buttercream cracking until about 2 months ago. I've increased my cake board thickness (now using 3/8" foam core) thinking that was the problem. I've stopped icing the crumb-coated cakes frozen thinking maybe the condensation from it thawing is making it crack (now just popping it in the freezer long enough to harden the crumb coat so I can put on the final coat). What is going on?

Anyone? Surely there's an easy fix I haven't tried!! Help!

I don't know if this would be an issue for you or not, but humidity plays a big factor for me. I live in the south and here it can go from 45 degrees in the morning to 82 and muggy in the afternoon. I have to be really careful and often have to adjust the temperature in my shop to keep it from happening to me.