I think this is where the cache is stored. I see one of the icons on the IRIS home page and the Cache File in the management portal matches exactly with the file name. Still confused as half of the webservers don't need this folder and seem to store it in /opt/webgateway/temp/. Exactly the same version/build.
I think this is a permissions issue as the ones who work out of the box, have apache:root as ownership of that folder, while the ones who don't have root:root.

These are kind of "citizen developers", using the folder structure using one namespace at a time. Each feature which they work on has its own namespace, which might be deleted when the feature is approved and merged into the main branch. They can understand that a namespace has been deleted, but not being able to select another one by using the normal VSCode UI will be a bad experience for them as this might happen quite regularly.

FYI

The codeQuality tool now requires a newer java version. I had to change this in the settings.json from

"sonarlint.ls.javaHome": "/Library/Java/JavaVirtualMachines/temurin-11.jdk/Contents/Home"

to 

"sonarlint.ls.javaHome": "/Library/Java/JavaVirtualMachines/temurin-21.jre/Contents/Home"

I skipped version 17 as there was already a 21 which seems to work OK.

I used the OpenJDK runtime:

https://adoptium.net/temurin/releases/