Nobody can help with the error information in that format; please see points 5 and 8 in Quinn’s Top Fourteen DevForums Tips.
But looking at the code, the signature for your delegate method isn’t correct:
func centralManager(_: CBCentralManager, didDiscover: CBPeripheral, advertisementData: [String: Any], rssi: NSNumber) -> [Int]
The return type of [Int] doesn’t match the protocol requirement (of no return type) and doesn’t make sense. This should have caused a compiler warning. If this method is actually getting called at run time, then the unexpected return value may cause undefined behavior, which could include sending your app off the rails with weird errors like that.
What is the purpose of return BeaconRSSI in that method? Where is it attempting to return that value to? Even if it weren't crashing, Core Bluetooth calls the delegate method just to inform you of something (discovery of a peripheral) and wouldn’t know what to do with any value returned from it.