Xiaomi vaccum prevented to call home - strange behaviour

Hello,

I ran an all ubiquiti network with the typical setup of IoT/NoT/normal VPN networks.

IoT devices can talk to the internet, but are limited to talk to the local LAN (e.g. Alexa, Netatmo and alike).
NoT devices can not talk to the internet, but only to HASS. All in seperate VLANs and respective firewall rules.

I have my xiaomi vaccum (roborock S6) inmy NoT network. I dont want him call back to china.

With doing so i see constant reestablishing of the wifi connection when the NoT firewall blocking rule is active. If I turn the rull off and the vaccum can talk home is is not restarting the wifi connection.

I tried in firewall rule drop or reject with both same results.

Is this expected? Has this an impact of my overall wifi performance? How do you have this setup?

Regards
Ralf