I just got a Forerunner 965. The WiFi client has problems with IP address assignments. It declines an IP address that it's used recently. It replies to the DCHPOFFER with a DHCPREQUEST followed by a DHCPDECLINE.
I suspect it acknowledges the IP address. Checks it with an ARP packet. Finds that the new IPv4 has been assigned to a host, without realizing the IPv4 was previously assigned to its own etheraddr.
It's a problem because I like to assign an IP address and a host name to my commonly used gadgets. This setup is working fine with a Garmin Index BP Monitor, a Garmin Forerunner 645, my phone, etc.
For the other half dozen people that can run a cron job on their Wifi access point something similar to:
*/5 * * * * ip neighbor delete 10.1.1.21 dev br-lan.10
is a work around. 10.1.1.21 and br-lan.10 would be changed for your environment.
I'd like to imagine this will eventually be called to the attention of the product technical staff.
