I haven't experienced that (yet). That portion has been pretty steady for us.
Here's some info regarding the DEP sync (from KB 21238):
By default, the AM server will update its DEP records from the Apple DEP web service every 24 hours. If you are making frequent DEP purchases, how can you force the LANrev server to update that data sooner?
There are 2 ways to update this data:
In the Admin console, run the "Synchronize Device Enrollment Data" command from the "Server" menu. If the Sync does not work, then try the "Reload Device Enrolment Data" option.
Alter the default sync interval that is implemented on the LANrev server.
To alter the default sync interval, implement the following preference value on the LANrev Server:
Type (Mac/Windows): Integer/DWORD
Default Value (in seconds): 86400
It is your choice to determine how frequently you would like this data to be updated; however, it is recommended to set the value to a timeframe that coincides with (or is slightly less than) your purchasing interval. For example, if you are adding new devices in your deploy.apple.com portal every hour, then you may choose to set this update interval to every 30 minutes.