My 5,1 has been upgraded to a newer Apple Broadcom BCM94360CD combination WiFi/Bluetooth card and now under High Sierra, it intermittently becomes unavailable (menubar icon changes to disabled, then eclipses, then back to available status). It happens about every 15 seconds. System Profiler correctly identifies the Bluetooth card and it's functionality. Under Sierra and older, it works fine. WiFi portion works fine in both High Sierra and previous OS X's. Since this is not a "supported" upgrade per se, I'm hesitant to report this bug unless others are also experiencing this issue. Is anyone else having the same problem?