If you are experiencing weird issues with Citrix connections in your LAN environment and you are using EDT, which is the preferred protocol in the newer versions of CVAD, this blog post by Thomas Kötzing is a must read:
Citrix, it’s time to fix three HDX things!
If you have your users on the newer VDAs and Workspace Client you can see their MTU in Monitor on Citrix DaaS. Unfortunately, HDX Direct relies on EDT so this could be a catch 22. If you suspect EDT is causing issues in your environment I would suggest setting up a test delivery group to help you sort out what’s going on. You can move a couple of users over that are experiencing the issues to verify.
Citrix HDX Direct for On Prem Access – IT-Adventures
Bypass Citrix Cloud Connectors with Rendezvous v2 – IT-Adventures