Had the same problem for long.
No one could give me an answer. Even certified technicians!
It was very frustrating and I was ready to throw the thing out of my window but I finally solved it
Here is what I did on my own.
Go to Config>DVR>Record - Turn ALL (Manual-Event-Timer) to CIF, click to save.
Again Config>DVR>Record - Turn ALL (Manual-Event-Timer) to 50fps, click to save.
Last Config>DVR>Record, select "Network First"
Click Yes to reboot
After that it was for the very first time that all cams kept a descent rate of fps (usually more than 12)
It looks like these machines have a crap processor that is not able to keep up feeding with descent rates of full promised fps in both network and recording.
I hope this will work for you.
