On a fairly popular site, there was a blog set up as a subfolder which ranked decently. If you searched for most keywords in any title, the respective page would generally appear at the top of the results as it should. In early July, the blog was changed and relaunched as a subdomain instead.
The background is that the main site was built in .NET and in an effort to have the blog run on a Linux server, it was only possibly by setting up a subdomain. The new blog looks great and had all content migrated over and 301ed old urls to the new urls. It's been about 2 months now, and I continue to notice that when searching for the title, the posts do not appear anywhere in visible site. Google does seem to be indexing all posts, but they are not ranking. Even though many of the old posts did not always rank super high, they could be found. I'm wondering if changing to the subdomain hurt that much or if its due to the main site having a similar problem.
Beginning in the second week of July, the main site's ranks plummetted. Similar problem as the pages are indexed, but very difficult to find whereas many appeared at the top of the results for several years.
June and July did bring a few messages in Google Webmaster Tools which I had never seen before including 'Increase in server errors',
'Increase in soft 404 errors', and 'Big traffic change for top URL'.
The server errors which Google reported to the main site were addressed in early August, but neither the main site nor the blog have seen the search traffic come back to normal levels.
Any insight would be appreciated. Has anyone seen this before as it doesn't seem to be anything related to the spammy links or disavow actions that so many others have faced with Penguin / Panda.