I have been having a similar issue with Horizon server 8.0 when clients were using client 8.0 and the web client. 

I upgraded to 8.4 server about a month ago and clients are using 8.0 in some cases and 8.8 in others for the full client and some are on the web client.  It doesn't seem to matter what client or server I am running.  Also the issue is very intermittent and seems to only effect a small sub set of users.  At the moment since 99% of my users connect from remote locations across the US and Canada I'm incline to point the finger at there ISP or issues on the internet. 

Today a client on one VM has reported disconnects by about 8 different users.  No other clients have reports issues. 

Reviewing the machine there have been some CPU spikes. 

There are about 20 users connected and only 2-5 loss connection at a time the others stay connected. 

there is no DRS/Vmotion happening on the machine either.