circuits are not both ready. Stalling conn.

Using an unstable (wifi) connection my Tor 0.4.0.0-alpha-dev client shows circuits are not both ready. Stalling conn. and most connections hang for some minutes until it let‘s through a bunch and hangs again.

It‘s confusing to see netflow padding while waiting for connections, looks like an instance of legacy/trac#23681 (moved).

Relevant code is around src/core/or/circuituse.c:3025. Log shows a lot of timeouts like:

Dec 30 10:48:14.000 [info] circuit_build_times_get_xm(): Xm mode #0: 325 75
Dec 30 10:48:14.000 [info] circuit_build_times_get_xm(): Xm mode #1: 375 47
Dec 30 10:48:14.000 [info] circuit_build_times_get_xm(): Xm mode #2: 325 75
Dec 30 10:48:14.000 [info] circuit_build_times_set_timeout_worker(): Circuit build measurement period of 1337373ms is more than twice the maximum build time we have ever observed. Capping it to 1143450ms.
Dec 30 10:48:14.000 [info] circuit_build_times_set_timeout(): Set circuit build timeout to 29s (28864.874645ms, 1143450.000000ms, Xm: 336, a: 0.361406, r: 0.282000) based on 1000 circuit times
Dec 30 10:48:14.000 [info] entry_guards_note_guard_success(): Recorded success for primary confirmed guard <scrubbed>
Dec 30 10:48:14.000 [info] circuit_build_no_more_hops(): circuit built!
Dec 30 10:48:14.000 [info] pathbias_count_build_success(): Got success count 209.532891/219.352138 for guard <scrubbed>
Dec 30 10:48:14.000 [info] connection_ap_handshake_attach_circuit(): Intro circ 4177057486 (id: 2028) present and awaiting ACK. Rend circuit 3511196698 (id: 2011). Stalling. (stream 41 sec old)
Dec 30 10:48:14.000 [info] or_state_save(): Saved state to "/var/lib/tor/state"
Dec 30 10:48:14.000 [info] rend_client_introduction_acked(): Got nack for [scrubbed] from [scrubbed]...
Dec 30 10:48:14.000 [info] rend_client_report_intro_point_failure(): 5 options left for [scrubbed].
Dec 30 10:48:14.000 [info] hs_client_reextend_intro_circuit(): Re-extending circ 4177057486, this time to [scrubbed].
Dec 30 10:48:14.000 [info] circuit_send_intermediate_onion_skin(): Sending extend relay cell.
Dec 30 10:48:14.000 [info] connection_ap_handshake_attach_circuit(): ready rend circ 3511196698 (id: 2011) already here. Nointro-ack yet on intro 4177057486 (id: 2028). (stream 41 sec old)
Dec 30 10:48:14.000 [info] connection_ap_handshake_attach_circuit(): Intro 4177057486 (id: 2028) and rend circuit 3511196698 (id: 2011) circuits are not both ready. Stalling conn. (41 sec old)
...
Dec 30 10:49:01.000 [info] connection_ap_handshake_attach_circuit(): Intro 4177057486 (id: 2028) and rend circuit 3511196698 (id: 2011) circuits are not both ready. Stalling conn. (88 sec old)
Dec 30 10:49:02.000 [info] connection_ap_handshake_attach_circuit(): ready rend circ 3511196698 (id: 2011) already here. Nointro-ack yet on intro 4177057486 (id: 2028). (stream 89 sec old)
Dec 30 10:49:02.000 [info] connection_ap_handshake_attach_circuit(): Intro 4177057486 (id: 2028) and rend circuit 3511196698 (id: 2011) circuits are not both ready. Stalling conn. (89 sec old)
Dec 30 10:49:03.000 [info] connection_ap_handshake_attach_circuit(): ready rend circ 3511196698 (id: 2011) already here. Nointro-ack yet on intro 4177057486 (id: 2028). (stream 90 sec old)
Dec 30 10:49:03.000 [info] connection_ap_handshake_attach_circuit(): Intro 4177057486 (id: 2028) and rend circuit 3511196698 (id: 2011) circuits are not both ready. Stalling conn. (90 sec old)
Dec 30 10:49:04.000 [info] channelpadding_send_padding_cell_for_callback(): Sending netflow keepalive on 608 to [scrubbed] ([scrubbed]) after 8689 ms. Delta 1ms
Dec 30 10:49:04.000 [info] connection_ap_handshake_attach_circuit(): ready rend circ 3511196698 (id: 2011) already here. Nointro-ack yet on intro 4177057486 (id: 2028). (stream 91 sec old)
Dec 30 10:49:04.000 [info] connection_ap_handshake_attach_circuit(): Intro 4177057486 (id: 2028) and rend circuit 3511196698 (id: 2011) circuits are not both ready. Stalling conn. (91 sec old)
Dec 30 10:49:05.000 [info] connection_ap_handshake_attach_circuit(): ready rend circ 3511196698 (id: 2011) already here. Nointro-ack yet on intro 4177057486 (id: 2028). (stream 92 sec old)
Dec 30 10:49:05.000 [info] connection_ap_handshake_attach_circuit(): Intro 4177057486 (id: 2028) and rend circuit 3511196698 (id: 2011) circuits are not both ready. Stalling conn. (92 sec old)
Dec 30 10:49:07.000 [info] connection_ap_handshake_attach_circuit(): ready rend circ 3511196698 (id: 2011) already here. Nointro-ack yet on intro 4177057486 (id: 2028). (stream 93 sec old)
Dec 30 10:49:07.000 [info] connection_ap_handshake_attach_circuit(): Intro 4177057486 (id: 2028) and rend circuit 3511196698 (id: 2011) circuits are not both ready. Stalling conn. (93 sec old)