Network neighbor in PCManFM works occasionally

My computer is in a local network. Occasionally I can visit the neighbor Windows computers by click “Network” in PCManFM. But sometime i just get a “Timeout has reached” dialog box. When “Network” doesn’t work, the neighbor computers can still be visited on other Windows computers.

A software which setups the iptables is running on my computer. I didn’t find any useful hint in its log.

Where is the log file of PCManFM?