It seems to me that the sb2 does not honor the lease-time of a DHCP
lease, i. e. when a lease has run out it won't rerequest a lease or
stop using the address. Rather, it will continue using the IP it got
during network setup indefinitely. IIRC I've reported the problem some
time ago. In the meantime I've changed the lease to never run out

But today I had to restart the sb2 because of an access point update.
It took quite some time for the DHCP request (normally it's instant)
and then "obtained" the IP

It's just that this address is in a reserved address space that I'm
_not using_ and my own DHCP server did not log a request for an
address. So either:

1) I have a rogue DHCP server on my network - worrisome
2) The sb2 gave up on the DHCP and fell back to a default address
- please don't. If this is really useful to anyone, please change the
message in that case from "obtained from DHCP" to "fell back to
default IP"

In any case, my sb2 shows this behaviour every second reset.