When you click on managed switch there is graphical interface in the top showing all interfaces icons and which interfaces are in use with connected devices, type of interface (ge/xe) and up/down status, etc. However, none of the switches in a site are reflecting this data, all ports show absolutely nothing - no connected devices nothing even in interface list option.

One of the possible reason for Mist UI icons not to display is when the devices are not properly sync’d to an NTP server. These switches happened to have the below logs flooding:

xntpd[yyyyy]: NTP Server x.x.x.x is Unreachable
xntpd[yyyyy]: NTP Server x.x.x.x is Unreachable

As soon as the NTP traffic was allowed through the Firewall, now all GUI interface for connected devices/ports started to work properly.