Zope 4.0 final was released this Friday as planned. Excellent!!! We had planned to release Plone 5.2 final as pending this weekend and do the official release of Plone 5.2 on May 20 (see Plone 5.2 Release Team Meeting, April 28, 2019). But unless we fix these issues we need to postpone the release. I myself was ill last week, am only now recovering and have very little time for this this week.
@Rotonen has already fixed those WebDAV issues, but was still checking if it is correct that plone.rfc822 gets bytes on 2.7, but strings on 3.7... or is there still something else.
Sooo. The last problem (TestATNewsItemFunctional) is not real-life issue since adding Archetypes News Items works fine with and without the modified response in the redirect. I spent most of today trying to find the cause and first had a couple of fistfights with CMFFormController (please die already!) and the Controller Python Script createObject.cpy which is used in that test. Turns out that was not the issue.
That finally led me down to Products.ATContentTypes.tool.factory.FactoryTool.__bobo_traverse__. That's a rather simple method that returns a temporary folder to hold the new item during creation but the %20 prevente it from finding the type.