Enabling the log
The main window has a log pane, or set the log level to warning (everyday) or debug (deep dives) in Parameter settings. Finer levels are noisier — set it back when you're done.
Recognize the key lines
accepted ... [proxy]: the request went through the proxy — normal.accepted ... [direct]: it went direct — if that's a site you wanted proxied, a routing rule matched wrong.rejected/failed to: the connection failed, usually followed by the reason (timeout, refused, DNS).
Typical readings
Lots of context deadline exceeded = timeouts, a node or line problem; connection refused = the target port is unreachable, usually a dead node or wrong port. Searching with these keywords, or switching nodes, beats guessing blindly.