I'd make sure to have a backup copy of your workbook made first, but then if you change your workbook to use "Offline Maps" and then publish to server just as a test (you can always delete the test workbook later) do you see a difference in results?
Typically maps reach out to Tableau maps server, though it is possible to host an "internal map server" if that's necessary for say security reasons. A common troubleshooting tool we use is to install Tableau Desktop onto one of the nodes in the Tableau cluster to see if the dashboard renders the same or if then experiences the same issue.
Lastly, we did recently move our maps proxy server so not sure if your IT team had whitelisted the older IP addresses:
Please refer --->6 Tips to Increase Dashboard Performance
I have created a Video on Performance recording
It is a way to analyse and improve the backend queries.
Thank you Ritesh, John and Mark, I will try to follow these tips and come back to you if the issue still persists.
I will first try changing the maps to offline ...the IT stuff seems to be little complicated or may be i need to read more on this