Before test, I configured DHCP and set lease time to 1h.
Rechecked FW 3.0.9, DHCP REQUEST flood occurs exactly after 30 min, first re-lease timing.
In FW 3.0.10, after 30 min, only 1 pair of DHCP REQUEST- DHCP ACK is logged... works as expected!
As far as I watched 3 times re-lease process loop, looks stable.

Thanks @emil, finally my flic buttons back to network!
Hope this FW solve @yea's and @Djelibeybi's problem too.

@Emil Wow, you are fast at work!
My HUB LR is #[MASKED]. I want to test it by all means. regards!

@Emil Maybe it is dhcp-8.1.9's bug, occurred on mine too.
Please check https://bugs.gentoo.org/766282 as similur situation, and publish FW with patched dhcpd if you could, as "easy way to solve it".
Thank you.