Tailscale being blocked by web shield (tailscaled process)

I have a Synology NAS with tailscale installed and connecting using the app installed on my laptop which has avast installed.

The connection appears to be working normally for small files.

However I am getting web shield popups from avast and unsure if it is signalling a real problem, or it is a false positive. I added the tailscaled program to exceptions but it still comes up. Screenshot of a typical alert attached, and the IP address does keep changing, which is odd. I have certificates installed on the NAS. Can anyone explain what is happening and if I should be worried? I note it is HTTP not HTTPS.