Not more than 30 devices able to connect

Hi, 

I am trying to connect multiple (around 30) wearable smart-belts to the Nighthawk XR500 router but there is the loss of connection frequently. When I check the logs there seem to be a large number of  ARP attacks. Something like shown below 

[DoS Attack: ARP Attack] from source: 10.0.0.12, Thursday, October 04, 2018 13:22:06
[DoS Attack: ARP Attack] from source: 10.0.0.12, Thursday, October 04, 2018 13:22:05
[DoS Attack: ARP Attack] from source: 10.0.0.15, Thursday, October 04, 2018 13:21:55
[DoS Attack: ARP Attack] from source: 10.0.0.15, Thursday, October 04, 2018 13:21:53
[DoS Attack: ARP Attack] from source: 10.0.0.6, Thursday, October 04, 2018 13:21:52
[DoS Attack: ARP Attack] from source: 10.0.0.15, Thursday, October 04, 2018 13:21:50
[DoS Attack: ARP Attack] from source: 10.0.0.6, Thursday, October 04, 2018 13:21:49
[DoS Attack: ARP Attack] from source: 10.0.0.15, Thursday, October 04, 2018 13:21:48
[DoS Attack: ARP Attack] from source: 10.0.0.15, Thursday, October 04, 2018 13:21:41
[DumaOS] DHCP lease change., Thursday, October 04, 2018 13:21:38

The smart-belt device uses an ATWINC1500-MR210PB wifi module with a SAMD21G microcontroller to send data at the rate of 3 KBps to the aws cloud via the MQTT server. What I am unable to understand is the reason for the router to treat the connection attempts from the belts as ARP attacks. 

Also, the logs keep showing DHCP lease changes happening for the smart-belt devices that are connected. My understanding, based on calls with NETGEAR customer support, is that the lease time is 24 hours. Not sure why so many new events for the DHCP lease change are happening. 

Any help would be highly appreciated. 

Thanks

Itmenon