We had some thing similar where users were complaining about disconnection of session and application not available. Opened a support case and they informed to update the VMtools to 10.1.15 and view agent to 7.3.2.After doing that we did not have any issues of application not available or disconnection in session.
Our Environment is
Horizon 7.2
RDSH hosts 2012 with app volumes integration
vSphere 6.5
Hope this helps