I think you’ve found many of the Android bluetooth issues that continue to haunt me. I do most of my Android testing and development on a Samsung Galaxy S6 Active running 6.0.1 and experience some of the same symptoms (rssi not updating, status 133 and -1, which refer to an unhelpful generic GATT error and a timeout respectively) from time to time. I don’t have much to add, because force closing the app, disabling and reenabling bluetooth is my usual panacea for these Android issues.
Slowly BLE on Android is getting more reliable… 4.4 was a nightmare, 6 is much improved but still far from perfect. Sorry I don’t have a fast answer on this one.