Hi again. I've updated the BTstack develop branch to compile against the 3.5.2 SDK. Unfortunately, BTstack doesn't get a response from the Broadcom Bluetooth chipset.
@redbear: Where's the version of BTstack that's used with the Arduino SDK? Does it use 3.3.1 or 3.5.2?
For now, you could use the 3.3.1 SDK with the ble-api-cleanup branch as it worked for me. You would also need the older version of RedBear's SDK fix for 3.3.1 - there's an 3.3.1 branch most likely for this.
I'll try to figure out what changed between the SDKs.