Client with low CBT can't establish any circuits

I ran my Tor client on my laptop for a while in a stable place. It ended up thinking my connection is super-fast:

Jun 21 01:49:15.786 [info] circuit_build_times_parse_state(): Loaded 1000/1000 values from 136 lines in circuit time histogram
Jun 21 01:49:15.786 [info] circuit_build_times_get_xm(): Xm mode #0: 575 55
Jun 21 01:49:15.786 [info] circuit_build_times_get_xm(): Xm mode #1: 625 51
Jun 21 01:49:15.786 [info] circuit_build_times_get_xm(): Xm mode #2: 575 55
Jun 21 01:49:15.786 [notice] Based on 1000 circuit times, it looks like we don't need to wait so long for circuits to finish. We will now assume a circuit is too slow to use after waiting 2 seconds.
Jun 21 01:49:15.786 [info] circuit_build_times_set_timeout(): Circuit timeout data: 2025.978516ms, 60000.000000ms, Xm: 590, a: 1.304577, r: 0.199000

But then I restarted my Tor, this time with a bridge that is in .za:

Jun 21 01:49:16.968 [debug] onion_pick_cpath_exit(): Launching a one-hop circuit for dir tunnel.
...
Jun 21 01:49:16.968 [notice] Bootstrapped 5%: Connecting to directory server.
...
Jun 21 01:49:16.968 [debug] circuit_handle_first_hop(): connecting in progress (or finished). Good.
...
Jun 21 01:49:17.256 [debug] connection_or_finished_connecting(): OR connect() to router at 196.x.x.x:10000 finished.
Jun 21 01:49:17.256 [notice] Bootstrapped 10%: Finishing handshake with directory server.
...
Jun 21 01:49:17.851 [debug] connection_tls_continue_handshake(): Done with initial SSL handshake (client-side). Requesting renegotiation.
...
Jun 21 01:49:18.448 [debug] connection_tls_finish_handshake(): tls handshake with 196.x.x.x done. verifying.
...
Jun 21 01:49:18.741 [info] command_process_versions_cell(): Negotiated version 2 with 196.x.x.x:10000; sending NETINFO.
...
Jun 21 01:49:18.741 [debug] circuit_send_next_onion_skin(): First skin; sending create cell.
Jun 21 01:49:18.741 [notice] Bootstrapped 15%: Establishing an encrypted directory connection.
...
Jun 21 01:49:18.969 [info] circuit_expire_building(): Abandoning circ 196.x.x.x:10000:54967 (state 0:doing handshakes, purpose 5)
Jun 21 01:49:18.969 [info] exit circ (length 1, last hop 0000000000000000000000000000000000000000): $0000000000000000000000000000000000000000(waiting for keys)
Jun 21 01:49:18.969 [info] circuit_build_failed(): Our circuit failed to get a response from the first hop (196.x.x.x:10000). I'm going to try to rotate to a better connection.
Jun 21 01:49:18.969 [info] connection_ap_fail_onehop(): Closing one-hop stream to '$0000000000000000000000000000000000000000/196.x.x.x' because the OR conn just failed.
...
Jun 21 01:49:18.970 [info] connection_dir_request_failed(): Giving up on directory server at '196.x.x.x'; retrying
...
Jun 21 01:49:27.978 [info] should_delay_dir_fetches(): delaying dir fetches (no running bridges known)

And now my Tor client is dead in the water.