There's a long thread over in the Mac mini forum about many people having Bluetooth issues (myself included). And, it seems that one of the issues may be that my Series 4 will only unlock my Mac mini maybe 1 out of 10 times on average. Everything is running the latest OS and I've rebooted the watch and Mac multiple times (to troubleshoot this problem or another problem or just during the course of my normal usage), but that doesn't seem to solve the problem. And, I've double checked the pref pane in Settings to make sure that I've set the watch to unlock the Mac. I've even unchecked it, rebooted and then checked it back on again, but with no real luck. Any ideas?