Citrix has released the following notification:
Citrix is aware of a potential issue impacting the Broker services on the Delivery Controller with the latest Microsoft Defender version (1.321.1319.0) update.
Citrix are currently investigating the root cause of this behavior. The behavior is currently impacting traditional deployments of Citrix Virtual Apps and Desktops and may potentially impact Citrix Virtual Apps and Desktops Service, when using Local Host Cache and Storefront.
The mitigation steps are available at the following Citrix Support article: https://support.citrix.com/article/CTX279897