I think you're probably ok and you can wait for the next update.... however, I wouldn't worry too much about PR, look at your SERP and traffic. Google doesn't really update pr that much anymore, if at all.
There are many reasons including to lost the Pr from upper to lower.So consider reasons for particular website why pagerank lower.
redirection from non www to www is required, pr will be up and down, dont worry for that just build link.
to overcome and better PR you need to build good traffic soon from now, google will again pay attention to you
In the last PR update my websites all dropped from PR3 to PR0 and one site went from PR4 to PR1. I still don't know what caused it. I didn't make any radical changes or bad seo. I think it may have been because I stopped updating it?