MR2100 - freezing when more than 20 devices are attached

Hi 

I have a new Nighthawk 2 with what looks like the latest firmware (NTGX24_10.17.01.00, which was updated on 2020/01/09) and it is the main router providing rural internet to quite a large network with circa 20-24 devices connected at any one time. I appreciate that this number of devices exceeds the recommended amount, but should this cause the device to freeze, where the LCD screen freezes, and occassionally the battery stops charging even though the power supply is attached). The router appears to operate normally when the numbner of devices is below 20, but the network the router is providing WiFi does need to cater for 20+ devices. 

Anyone come across this problem before? 

All help appreciated!