Servers not polling

I tried to search the forum for this issue but I couldn't find anything similiar to what I am experiencing.

I have a few servers that I have added to monitor. They add properly and I can view them under the "maps" tab. But when I click on the server the dials do not appear and there is no polling data for the server.

If I click edit for "cpu utilization" and then click test - the test passes and the dial shows up until the next poll interval. Once the next poll interval runs the dial disappears and it doesn't receive any information.

Most of the servers work fine but a few of them have this issue.

I've tried removing / re-adding / restarting the machine / reparing the database.

Any ideas?