If disk cache feature is enabled when creating machine catalog, system hang issue may occur on VDA version 1912 or later version.
 

Citrix recommends that you reevaluate the disk size to ensure that it has sufficient disk space for the allocated workflow and additional pagefile size.
The pagefile size is typically related to the amount of system RAM.
If the existing catalog disk size is insufficient, create a new machine catalog and allocate a larger write cache disk.

Example:
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VM memory size: 8GB
RAM cache size: 1GB
Cache disk size: 20GB
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Problem Cause

VDA version 1912 or later version implements new Machine Creation Services Cache Driver CVhdFilter.sys (Previously CtxMcsWbc.sys), which is based on VHDX.
It supports file-based write cache technology, providing better performance and stability. The new functionality provided by MCS I/O could require a higher write cache storage requirement compared to previous Citrix Virtual Apps and Desktops releases.

Since the new Machine Creation Services Cache Driver CVhdFilter.sys reserves 2MB blocks on the VHDX write cache, the cache file could grow much larger and much faster than the previous driver(CtxMcsWbc.sys).  
If the write disk size is insufficient, you may encounter issues such as system thread is pending on disk IRP, and all queued disk IRPs are pending on CVhdFilter.sys. 

 

https://docs.citrix.com/en-us/citrix-virtual-apps-desktops/1912-ltsr/install-configure/machine-catalogs-create.html#overview

MCS storage optimization changed with Citrix Virtual Apps and Desktops version 1912 LTSR. This release supports file-based write cache technology, providing better performance and stability. The new functionality provided by MCS I/O could require a higher write cache storage requirement compared to previous Citrix Virtual Apps and Desktops releases. Citrix recommends that you reevaluate the disk size to ensure that it has sufficient disk space for the allocated workflow and additional pagefile size. The pagefile size is typically related to the amount of system RAM. If the existing catalog disk size is insufficient, create a new machine catalog and allocate a larger write cache disk.