Try to remove this part:

// Start GATT server
rc = ble_gatts_start();
if (rc != 0) {
ESP_LOGE(TAG, "GATT start failed: %d", rc);
return;

Honestly I haven't fully checked the underlying cause yet.
Apparently, `nimble_port_run` calls `ble_gatts_start` which leads to some sort of memory corruption ...