I wrote 2 times when i had the same problem with my site 3 months ago it was the first time it happened , after a week without doing any changes it came back, in 3 weeks it happened aggain that's when i noticed the url for articles on the home page where followed so i changed them into nofollow urls and site came back within a day, now after 1 month and a half after i thought i solved my problems it happened again. Same sypmtoms: pr stayed the same it even increased in the past 3 months, all pages are indexed and still indexes new pages, major keywords are gone(ex:mesothelioma treatment was #7, mesothelioma cancer was #23, asbestos cancer was # 33), i have very few traffic here is my site: www.mesotheliomatreatmentcenters.org Why is this happening???
SERP algorithms are different from se to se. Some new sites may come above urs then SERP may change. Check Any out going link is banned by Google. If yes then remove the banned links soon. Create more Quality One Way Links. Use offPage SEO tactics.