Model : Archer MR200

Hardware Version :

Firmware Version :

ISP :

I have an Archer MR200 and have been trying to collect statistics from this router for each device on my network that accesses the internet through it. Initially I found that, when using DHCP to assign IP addresses to all devices on the network from the MR200, the router was not collecting statistics correctly when the IP address changed for a specific device. I also noticed that for devices that are connecting to other routers on the network which are then connecting wirelessly to the MR200 that it is the MAC address of this other router that is being identified along with the IP address of the device in the MR200 statistics page and thought that this may be interfering with the collected statistics.
I have now reserved IP addresses for each device on the network so that they always get the same IP address from DHCP on the MR200 and this seemed to be working better after deleting the statistics and rebooting. However, I have now noticed that, even though the devices are now getting the same IP address, the statistics sometimes seem to reset so that the cumulative value for that device is set to 0 and starts accumulating again. This throws out the total cumulative statistics that I am trying to record for each month’s data usage.
Is there a way to ensure that the statistics accumulate consistently for all devices over the monthly allowance period (I have set the monthly allowance period on the MR200 successfully) or is there a fault with my MR200?