NVR Services can restart for a number of reasons. Most commonly they are of no concern. Updating NVR software, changing network settings, adjusting time, enabling storage drives; all of these can report a service restart in the logs.
If the NVR is behaving poorly and there are line items of "X service Terminated Abnormally", this is indicating that an error has occurred and the service needed to stop. The service will start on its own and continue running.
If there are a large number of Abnormal terminates then it may point to an error in NVR configuration, system drive failure, or other issues.
If this is the case, please contact support.