DAWN roaming doesn't work due to umdns failing to start


I know I'm new here, but I've already read existing topics about umdns failing to start and I seem to have a different problem.

I run 3 Archer C7 devices - one as main router+AP and two as "dumb" APs. Two of these are v5 and one is v4.

Using Luci, I've installed and enabled 802.11r and DAWN for 802.11k and 802.11v. It works properly between v4 and one of v5 Archers - I can see both Hearing Map and Network Overview and they contain information about the other neighbour.

The problem is that the second v5 Archer doesn't participate in the exchange - DAWN's Hearing Map and Network Overview only show locally connected clients and no information from other routers is visible (other routers also don't see anything about the problematic one).

I think this is caused by umdns failing to start, it seems to segfault:

[   43.325054] do_page_fault(): sending SIGSEGV to umdns for invalid read access from 00000000
[   43.333733] epc = 004039d9 in umdns[400000+6000]
[   43.338738] ra  = 004039d3 in umdns[400000+6000]

I'm completely puzzled because both routers are v5 and both have mostly the same configuration -- latest OpenWrt 21.0.x installed and only differences are that one of them has WAN disabled since it's a "dumb" AP and the other (non-working) one is used as main router.

I'd highly appreciate any pointers to what I can do to debug and fix this? Some details follow:

root@ruter:~# cat /etc/config/umdns
config umdns
        option jail 1
        list network lan
        list network 'wan'

I've already renamed /etc/seccomp/umdns.json to /etc/seccomp/umdns1.json so it doesn't seem to be the seccomp issue.

Any pointers?