This is more a reminder for me when it happens to me again. I recently deployed Horizon 7.4 for a customer using a bunch of nVidia Grid cards in Dell 7910 rack workstations - they were previously using Horizon 6, with the direct connection agent and all was good.
I deployed connection servers, UAGs and all the good stuff, created desktop pools and updated the image from the Horizon 6 Direct Connect agent to the latest 7.4 agent. We also updated the nVidia software to the latest version.
First problem that we hit on was that their application could no longer communicate with the SQL database instance on the same VM. A little troubleshooting led me to the fact that the Horizon 7.4 agent seemed to be interfering with these comms. I should have raised a support case for this (as this shouldn't be happening!), but time was of the essence and we knew that the v6 agent didn't do this.
We rolled back to the latest version of the v6 agent (6.2.6, from memory) and the app worked fine in the VDI image - happy days! On the downside, we found that the VDI resolution was now no longer scaling to meet the resolution of the client screen, and was fixed at the native resolution in the VM - this was happening both with the Horizon client and BLAST clients.
A bit of chat in the vExpert Slack EUC channel suggested that I may have made an error when rolling back the agent - you must remove Horizon agent, nVidia drivers and then VMware tools before reinstalling in the reverse order. I ran through this, as well as verifying the nVidia VIB in the hosts was the correct version for the drivers but had the same issue once more.
Long story short then: we rolled back to the Horizon 6.0 agent and all worked perfectly (even though we we running 7.4 Connection Servers). Next time I'm with that customer I'm going to suggest that they raise their issues with both the 6.2.6 agent and 7.4 agent as obviously the 6.0 agent will go end of support before the rest of their environment, however I wanted to get this written down in case it helps anyone else in future.