What Service Release of QVS11.20 are you running? If you do not know, open QMC and goto QMC->System->About. Scroll down until you encounter information about QlikView Server and look for the "Product Version". The version number can be translated into a SR.
IE11 is supported by QlikView Server from SR5 on. I suggest you upgrade your server to SR11.
Thanks Peter for the reply (sorry, I have been out of action for a couple of months),
The Product Version according to QMC is 11.20.11922.0
The help file says "QlikView 11.20 SR8".
Since my original post, we have found that we can use the IE11 Enterprise Mode as a work around.
Edit: One of the challenges has been to find the full version including the SR#. The help file launched from the console says 'QlikView Management Console, Version 11.20 SR2 (build 11922)', so it looks like an upgrade is in order.
Indeed, it's quite a challenge to find out which SRx your server is running. IIRC there is a list somewhere in the Resource Library of build numbers and Service Release numbers. An incomplete one can be found in this discussion: Client Build Number and version relation
11.20.11922 corresponds to QlikView 11.20SR2. SR8 has build number 11.20.12577