Here, a user reported a failure to connect to their own bridge, stopping at 25% bootstrapped. teor and I went through the basic troubleshooting steps of checking the bridge syntax, system time, and firewall settings. With or without obfs4 didn't make a difference. The user eventually tried downgrading the bridge from 0.3.4.9 to 0.2.9.17--and that fixed it. Their client version was 0.3.4.9. https://bugs.torproject.org/28717#comment:18
They also tried with two bridges from BridgeDB. The one running 0.3.4.9 didn't work, and the one running 0.2.9.17 did.
A possible lead are these client log messages: [info] handle_response_fetch_desc(): Received server info (body size 0) from server 'X.X.X.X:YYYY' [info] handle_response_fetch_desc(): Received http status code 404 ("Servers unavailable") from server 'X.X.X.X:YYYY' while fetching "/tor/server/authority.z". I'll try again soon.