When something breaks, don't rush to swap nodes — read the log first. The lower half of v2rayN's main window is the live log, and you can raise it to “Debug” for more detail.
Common keywords
failed to start: address already in use: local port taken — change the port or kill the process holding it.context deadline exceeded/i/o timeout: timed out reaching the server, usually a dead node or local network issue.tls: handshake failure/certificate: TLS handshake failed — check SNI, certificate, clock, or whether the REALITY parameters are right.rejected/invalid user: authentication failed — wrong UUID / password.connection reset by peer: the far end reset the connection, possibly interference or a server policy.
Enabling debug logs
Settings → Parameter settings, set the log level to debug and restart the proxy. Switch back to warning afterwards — debug writes a lot.
Before posting logs for help, redact the UUID, domains and IPs — they're effectively your account credentials.