Hi,
Have you configured all the clients to take definitions from SEPM. If yes, then you can change a policy in SEPM, and monitor the time in which it gets implememted at the clients. If the policy gets deployed immediately, then its not the communication issue.
If the communication is fine, then you can re-download the definitions at SEPM. And let us know if that helps to solve your issue.
Cheers,
Aniket