BLE connections to STM32WB15 always fail with error 0x3E

[HHunt.1]

I'm writing firmware for a custom board using the STM32WB15CCU6E and am having trouble getting the BLE functionality to work properly. I have created a minimal project that gets BLE running, and have not changed anything in the STM32_WPAN section, so it's just running the default "Custom P2P Server".

The device advertises and is picked up by Windows and Android, but connection attempts always fail. During a connection attempt, HCI_LE_CONNECTION_COMPLETE_SUBEVT_CODE is received (in app_ble.c) with a Status of 0, and HCI_DISCONNECTION_COMPLETE_EVT_CODE is then received immediately after with a Reason of 0x3E (connection failed to be established).

Sniffing the packets shows that the master sends CONNECT_IND and then makes repeated requests with LL_FEATURE_REQ, but the slave never sends anything back. The slave then goes back to advertising a few seconds later.

I've been working on this issue for multiple days now and am out of ideas, so would really appreciate some help solving it.

[HHunt.1]

Problem was solved by setting CFG_BLE_LSE_SOURCE to Enabled in CubeMX, as mentioned in https://community.st.com/s/question/0D50X0000C3BaK3SQK/migration-from-nucleo-to-my-own-board-doesnt-work. I had already switched RFWKP from LSE to HSE in Clock Configuration (as we do not have an LSE on our board), but this does not work without also changing CFG_BLE_LSE_SOURCE to match.