If Qlik Sense server is upgraded to November 2018 will existing extensions installed on the server and used in applications keep working or will they be removed during the upgrade (from September 2018)?
This highly depends on each extension, most probably is that all extensions working in September 2018 also works in November 2018, as it is a small step and from the most recent versions.
Maybe you can try each of the used extensions in a desktop version to test them before upgrading the server.
When dealing with extensions and upgrades to server I would only be using extensions that are either
1. Approved under the approved extension program 2. Have been around for awhile and have visible signs of being supported if issues have occurred due to upgrades. Look at the comments against the extension to see history of its use. 3. Write it yourself and understand it enough to be able to alter it should the upgrade cause it to break.
Have a test app that contains all your production extensions so you can run it on your upgraded test/dev server and check this before proceeding with release to production
