We have a total of 22 DC's in our ADManager and syncing data from them all but i have a couple DC's that are just refusing to sync.

When i run a report about inactive users, for example, the whole remote site shows up as inactive as ADManager cannot pull data from the DC they are checking in with. 

I have checked everything and cannot find any issues or differences from the others that are working.

Is there a log i can check to try and identify the issue?