TEMP environment setting changing to "local_" folder

Hi
We have FSLogix in place which is supposed to be only implemented when users log on to our Citrix servers - this was set up by someone else so I'm not fully familiar with it.
We have a strange issue with some pcs/laptops and some users. When they log on, their environment variables for TMP and TEMP are changing to c:\users\local_user.name" which doesn't exist on the pc/laptop so some apps stop working until we set these back to the user's actual profile folder. I can view these settings in the registry under HKCU\Environment - TMP & TEMP
I can't work out how this setting is being changed. I don't see any GPO setting that could be forcing the change. I can manually change the setting but it is being updated again the next time the person connects to the network and logs on.
I'm also assuming it's something to do with FSLogix as the "local_user.name" folders are created and used on the Citrix servers when users log on.
Has anyone seen a similar issue and can advise ?
Thanks