Hi,

If the master VM of the instant clone has many snapshots, the image push of the instant clone will take longer.
A slow image push will result in a timeout, so in this regard, it is not a mistake to say that Horizon's performance will be degraded if there are many snapshots.

However, I believe that the black screen is caused by the Horizon Agent's video driver (SVGA , Indirect display driver).

Also, to examine the black screen event in detail, it would be useful to implement method2 of KB2078739.

VMware Horizon and VMware Tools SVGA Driver Compatibility. (2078739)
https://kb.vmware.com/s/article/2078739

Additionally, if you are using PCoIP, you should check if the same problem occurs with VMware Blast.
It seems to me that maybe VMware Blast would not cause the problem.