Hi sonikapoor1804
Is this issue happening only after upgrading horizon client?
Did you also perform upgrade on actual view connection servers or view agent on gold image?
The error generally comes either due to port being blocked (depending upon the protocol used)Or display driver issue. For port issue, you can isolate the issue by first connecting to VDI using connection server URL internally and see if that works or not. If that works and issue happens only when you are coming through any load balancer or a gateway (UAG/Security server), chances are ports are being blocked. Please review below few KBs to isolate further:
VMware Knowledge Base