Receiving Flow / Not Receiving Flows

We currently have Netflow v9.6 and and I receive random e-mail notifications from Netflow stating that it's not receiving Flows from a particular remote router interfaces (mostly LAN, sometimes WAN). 15 minutes later, I receive another e-mail stating that it's receiving flows once again. During this time, there is WAN no outage... just not receiving flows.

We have ~55 remote routers that we monitor using Netflow but only this device reports issues. I've had our managed service provider check the router config and they confirm it's the same as other sites. When this problem started several months ago, they upgraded to IOS 12.4 at my request. The problem still persisted afterwards.

This device will sometimes go days / weeks without any issue and then start notifying us it's not collecting data. Afterwards, it will be silent again for an undetermined period of time.

Any help is greatly appreciated.