I'm in the same situation Jake. I was ready to build a privacy wall/pergola and can't get the lumber. Oddly, the company that just built my new deck didn't have any issues.
The story I heard was that there is a Canadian company that makes a lot of the chemicals to do the pressure treating and they were shut down for almost 2 months and that caused a huge delay in a lot of the pressure treated stuff. But I haven't verified that or seen it otherwise.