What it the meaning of "ReceiveIPv4 is not running"

I have two machine in tailscale network, run tailscale status in one, it reports

Health check:

- ReceiveIPv4 is not running

what is the meaning? another machine doesn’t has it, I open port 41641 in another machine, but p2p connect between them is not stable, most of time need relay.

Thanks very much for your help