Merged Projects in RH 2019

Has anyone tried to work with merged projects in RH 2019? I am running into some weird issues and I can't get merged help to work regardless of the way I try it.

I tested the following.

• Creating merged project (a parent with one child) in RH 2019 Classic - OK. Opening index.htm from the parent displays the TOC of the parent and child modules and all their topics.
• Creating merged project in RH 2019 - NOK, the TOC only shows the current project. If you open index.htm from the parent, you only see the parent topics; if you open index.htm from the child, you only see the child topics. If you open the child project and click a topic different from the default one, the TOC of the parent is automatically loaded and replaces the TOC of the child. This happens when the URL changes from file:///C:/master_new_resp/mergedProjects/child/index.htm#t=First_Merged_Topic.htm to file:///C:/master_new_resp/index.htm#t=mergedProjects%2Fchild%2FSecond%20Merged%20Topic.htm. Other than that, you can navigate without errors among the displayed topics in either parent or child.
• Upgrading merged project from RH 2019 Classic to RH 2019 - NOK, same behavior as the new project above.
• Upgrading our existing source files from RH 2017 to RH 2019 - NOK, even weirder. If you open index.htm from the parent, you only see the parent topics and you can correctly navigate through the parent's topics. If you open index.htm from the child, you only see the child topics, but once you click any of the topics you get an error saying that the file does not exist. (All the topics do exist and can be opened standalone, but once you click the link that should show them in context, with TOC, the error appears again.) The problem seems to show up when the URL switches from file:///C:/responsive_new/mergedProjects/child_project/index.htm#t=Child_Topic1.htm to file:///C:/responsive_new/index.htm#t=mergedProjects%2Fchild_project%2FChildTopic2.htm.

All the above happen for both WebHelp and Responsive, using the Azure layout.

I guess that something went wrong in the upgrade, but I can't even understand how merged projects are supposed to work in 2019 to know what I should be aiming for...