panicked at 'unexpected event 59'

[HaoboGu]

Recently I encountered some runtime panics, the following is the log:

DEBUG on_data_length_update conn_handle=4 max_rx_octets=251 max_rx_time_us=2120 max_tx_octets=251 max_tx_time_us=2120
└─ nrf_softdevice::ble::gap::on_evt @ /Users/haobogu/.cargo/git/checkouts/nrf-softdevice-03ef4aef10e777e4/d5f023b/nrf-softdevice/src/fmt.rs:125 
DEBUG on_conn_param_update conn_handle=4 conn_sup_timeout=100 max_conn_interval=12 min_conn_interval=12 slave_latency=4
└─ nrf_softdevice::ble::gap::on_evt @ /Users/haobogu/.cargo/git/checkouts/nrf-softdevice-03ef4aef10e777e4/d5f023b/nrf-softdevice/src/fmt.rs:125 
ERROR panicked at 'unexpected event 59'
└─ nrf_softdevice::ble::gatt_client::att_mtu_exchange::{async_fn#0}::{closure#2} @ /Users/haobogu/.cargo/git/checkouts/nrf-softdevice-03ef4aef10e777e4/d5f023b/nrf-softdevice/src/fmt.rs:101 
ERROR panicked at /Users/haobogu/.cargo/registry/src/rsproxy.cn-0dccff568467c15b/defmt-0.3.10/src/lib.rs:380:5:
explicit panic
└─ panic_probe::print_defmt::print @ /Users/haobogu/.cargo/registry/src/rsproxy.cn-0dccff568467c15b/panic-probe-0.3.2/src/lib.rs:104 

It seems that there's a timeout when exchanging mtu:

nrf-softdevice/nrf-softdevice/src/ble/gatt_client.rs

Lines 589 to 608 in b53991e

	portal(conn_handle)
	.wait_once(|ble_evt| unsafe {
	match (*ble_evt).header.evt_id as u32 {
	raw::BLE_GAP_EVTS_BLE_GAP_EVT_DISCONNECTED => return Err(MtuExchangeError::Disconnected),
	raw::BLE_GATTC_EVTS_BLE_GATTC_EVT_EXCHANGE_MTU_RSP => {
	let gattc_evt = match check_status(ble_evt) {
	Ok(evt) => evt,
	Err(e) => return Err(e.into()),
	};
	let params = get_union_field(ble_evt, &gattc_evt.params.exchange_mtu_rsp);
	let mtu = params.server_rx_mtu;
	debug!("att mtu exchange: got mtu {:?}", mtu);
	conn.with_state(|state| state.att_mtu = mtu);
	Ok(())
	}
	e => panic!("unexpected event {}", e),
	}
	})
	.await

Is there any methods to avoid this panic or manually handle it?