Just received the news that there will probably be a new path release (3.1.2) in September fixing some Session 0 issues.
I recently came across some problems with the use of session 0 in ApEx. My first problem was with the use of public pages and an Authentication Scheme current to Application Express. I kept getting the next error while branching:
The requested URL /pls/apexsaas2/wwv_flow.accept was not found on this server.
So actually a 404 Not Found error. Scott Spadafore acknowledged the problem on the Oracle Forum and said it could be fixed in the next patch release.
My other problem with the use of session 0 was with a rewrite rule for a domainname. A Polish ApEx Application (Yes: ApEx can work easily with other languages) could not be found because we kept getting a 404 Not Found Error, it would only work if you refresh the page each time in Internet Explorer.
Metalink note 468402.1 (HTTP 404 notfound error when trying to access a page by using zero session id) described the exact problem for us but the workaround could not be applied in our case.
Production management of Oracle advised us to wait until the next patch release in September.