[atlas] Probe marked as offline, but it's online...

Hello Atlas users!

I've connected my probe to a new network environment, to test everything 
before the big migration starts. It came up again immediately and 
displayed it's new network details at the WebUI. For the first time 
there was an IPv6-ULA prefix visible. The router (OpenWrt 15.05) 
supports full IPv6 via tunnel, but it's not advertised to the probe's 
VLAN and blocked by firewall rules. Everything seems to work, good!

I've switched it off/on for several times, went back to the old 
router/modem and powered it on again. After some hours I've checked the 
WebUI again: My probe is offline! :-(

I've tested it again on the new router: Offline! Once again on the old 
setup: Offline! Untouched default router/modem from my ISP: Offline!

Current LED status: (from 1-5; power to button)

> on
> off
> slow blink
> on
> on

SOS-DNS-history from Wireshark: (switch port mirrored to my analysis 
interface)

> Standard query 0x0002  AAAA U.*************.sos.atlas.ripe.net
> Standard query response 0x0002  AAAA 2001:67c:2e8:11::c100:1337
> Standard query 0x0003  A U.*************.sos.atlas.ripe.net
> Standard query response 0x0003  A 193.0.19.55

The probe is online and communicates with many servers. Looks like the 
built-in tests are running fine. There is NTP, DNS, ICMP, UDP and HTTP 
traffic. But it's still offline at the WebUI.

I've double and triple checked everything on my side. Any ideas what's 
going wrong?

-- 
With kind regards,
Christian Schrötter