%ZEN.Dialog.namespaceSelect is not showing in some namespaces and giving a 403 Page not found error. Any ideas what could be wrong?

I have an issue and can't seem to find the problem.

Issue

 In some namespaces i get a 403 Page not Found error for healthconnect/csp/healthshare/[NAMESPACE]/%25ZEN.Dialog.namespaceSelect.cls ; healthconnect/csp/healthshare/[NAMESPACE]/%25ZEN.Dialog.finderDialog.zen  && healthconnect/csp/healthshare/[NAMESPACE]/_CSP.UI.Portal.About.zen

Iris setup

It is currently configured in a mirror group and on the other mirror-member i don't encounter the issue. (I have checked if it was because of the member-type Primary and Backup). 

The user that I am using has the %All role. So this kind of excludes an issue with permissions.

What I checked

I checked if there was any difference between the 2 mirror members (working HLT01 and not working HLT02) for the following things:

1. The IIS
2. The Web Gateway
3. The Web Applications
4. Mappings

I also did a compare for the above items with the namespaces that do work. But it didn't show any differences that would contribute to the error, as far as i could see.

I also did the following:

1.  Imported the Security settings from the HLT01 into the HLT02
2. Again set the not working namespaces to interop via the Terminal command
3. Checked what namespaces worked and once that didn't for the URLs.
4. Checking when the HLT02 was a Primary member-type
5. Re compiling all the code of the not working namespaces

Hope someone can help.