Tuya: Devices are unavailable, but firewall between HAOS and device is open?

Hej,

(still doing first steps with HAOS).

I can see my Tuya dehumifier being connected and available on my Ruckus WLAN APs. I am able to control the Tuya device using the Tuya Smart app on my mobile phone.

However the device and entities are reported unavailable in HAOS, Tuya Cloud integration. HAOS is located on another OPNSense firewall port using a different network than the APs and the mobile phone - but firewall rules are identical:

I do allow IPv4 TCP/UDP from HAOS server to any, ports 6608, 6667-6669, 6681, 6682, 8883, 12121, 12122, 12746 and 40000-41000 according to the Tuya developer documentation.
The rule is the same on both LAN and SMARTHOME ports, one is working, one is not.

What else can I check/validate to get the Tuya working fine?