DHCP issues coincided with ARP issues. When roaming between access points, IP addresses (and associated ARP requests) were sent to the wrong switch ports, so they did not reach the access points the devices were roaming to. This caused the roamer to lose its IP after a few seconds and it could take up to 90 seconds to get the IP back (even with manual issuance/renewal). Also, ARP requests for this device no longer work. I simply restored the MAC address not found or nothing at all.
This had to do with a bug in the UDM-Pro firmware, where the Ethernet and SFP ports are not actually on one switch, but are forwarded internally by the software.
So something went wrong here, causing the SFP-connected and Ethernet-connected switches to not work well together. The solution was this: connect one big switch via SFP and connect everything to it, but of course this is not a solid solution.
In the end, Ubiquiti released a firmware fix for this.
Regarding DNS, it is very stable nowadays, but in the past there were a lot of problems where clear-robin didn’t work properly (so after record expired it stayed in cache), Round-robin DNS didn’t work, and many Of strange problems (so this has to do with the internal DNS server).
I also have to knock on the door, because I haven’t had any (big) problems in the past six months, other than the inconspicuous bugs in the early release firmware (which you can expect), especially in UniFi Protect.
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