conn failed to establish. RF noise?

[Hayden Ball]

We're seeing the following intermittently while attempting to connect from a Mac/iOS Central.

Using Android as a Central does not produce the same error.

[00:00:33.054,656] <wrn> bt_conn: conn 0x20003878 failed to establish. RF noise?
[00:00:33.054,931] <inf> bluetooth: Disconnected (reason 0x3e)

[00:00:34.374,511] <wrn> bt_conn: conn 0x20003878 failed to establish. RF noise?
[00:00:34.374,816] <inf> bluetooth: Disconnected (reason 0x3e)

[00:00:34.644,561] <wrn> bt_conn: conn 0x20003878 failed to establish. RF noise?
[00:00:34.644,836] <inf> bluetooth: Disconnected (reason 0x3e)

[00:00:35.154,479] <wrn> bt_conn: conn 0x20003878 failed to establish. RF noise?
[00:00:35.154,754] <inf> bluetooth: Disconnected (reason 0x3e)

[00:00:35.334,289] <wrn> bt_conn: conn 0x20003878 failed to establish. RF noise?
[00:00:35.334,564] <inf> bluetooth: Disconnected (reason 0x3e)

[00:00:35.724,487] <wrn> bt_conn: conn 0x20003878 failed to establish. RF noise?
[00:00:35.724,761] <inf> bluetooth: Disconnected (reason 0x3e)

[00:00:36.114,410] <wrn> bt_conn: conn 0x20003878 failed to establish. RF noise?
[00:00:36.114,685] <inf> bluetooth: Disconnected (reason 0x3e)

[00:00:36.505,371] <wrn> bt_conn: conn 0x20003878 failed to establish. RF noise?
[00:00:36.505,645] <inf> bluetooth: Disconnected (reason 0x3e)

[00:00:36.685,363] <wrn> bt_conn: conn 0x20003878 failed to establish. RF noise?
[00:00:36.685,638] <inf> bluetooth: Disconnected (reason 0x3e)

[00:00:37.282,043] <wrn> bt_l2cap: Ignoring data for unknown channel ID 0x003a
[00:00:38.182,312] <inf> bluetooth: Disconnected (reason 0x13)

Sometimes the connection eventually establishes, sometimes it doesn't.

Running the BT peripheral sample, the error does not occur.

Are you able to suggest any debugging steps, please, or suggestions as to why the behaviour might be different with the two centrals?

[Hayden Ball]

Okay, yes.

This can be easily reproduced using the extended_adv advertiser sample:

west build -b nrf21540dk/nrf52840 zephyr/samples/bluetooth/extended_adv/advertiser -DCONFIG_LOG=y -DCONFIG_SHELL=y
west flash

[00:01:11.272,644] <wrn> bt_conn: conn 0x20002920 failed to establish. RF noise?
Disconnected, reason 0x3E
Connection object available from previous conn. Disconnect is complete!
Remote disconnected early...
Disconnected state! Restarting advertising
Starting Extended Advertising
Connected (err 0x00)
Connected state!
Initiating disconnect within 5 seconds...
[00:01:11.452,545] <wrn> bt_conn: conn 0x20002920 failed to establish. RF noise?
Disconnected, reason 0x3E
Connection object available from previous conn. Disconnect is complete!
Remote disconnected early...
Disconnected state! Restarting advertising
Starting Extended Advertising
Connected (err 0x00)
Connected state!
Initiating disconnect within 5 seconds...
[00:01:11.961,669] <wrn> bt_conn: conn 0x20002920 failed to establish. RF noise?
Disconnected, reason 0x3E
Connection object available from previous conn. Disconnect is complete!
Remote disconnected early...
Disconnected state! Restarting advertising
Starting Extended Advertising
Connected (err 0x00)
Connected state!
Initiating disconnect within 5 seconds...
[00:01:12.442,321] <wrn> bt_conn: conn 0x20002920 failed to establish. RF noise?
Disconnected, reason 0x3E
Connection object available from previous conn. Disconnect is complete!
Remote disconnected early...
Disconnected state! Restarting advertising
Starting Extended Advertising
Connected (err 0x00)
Connected state!
Initiating disconnect within 5 seconds...