R7800 Showing Multiple DHCP Lease Events at Renewal

TL;DR Those DHCP logs are not necessarily address lease renewals; the device could be requesting other information.  The router will log any request.  Just ignore them.

Many people think of DHCP as just the protocol for handling dynamic IP addresses, but it can do so much more than that.  Look at all of the options that can be included in a DHCP packet.  The common options are IP address, subnet mask, default gateway and DNS servers.  Some devices can and will send DHCP packets to the DHCP server to request other information besides these common options.  If you are curious, you can run Wireshark to see exactly the device is asking for.  The DHCP server in the router will not necessarily be able to handle these other options, but it will respond with whatever information it can provide.   On Netgear routers, this will always appear in the logs as a DHCP message.

Additionally, DHCP is a device-driven protocol.  The device always initiates the request.  The router is passive.  Despite any differences in the frequency of DHCP messages observed between a R7000 and a R7800, it's not due to the routers.

It can be a nuisance to see so many DHCP messages in the logs but you can ignore them.  It's very unlikely that the connection drop on a wireless device was caused by them.  More likely, the wireless device lost its connection because it was too far away or the signal was otherwise disrupted.  Once the device re-established the connection, it immediately asked for a dynamic IP address.