Mac and iPhones not detected on Airdrop

I am using a 13-in MacBook Pro Mid 2012 running on v10.11.4 (OS X El Capitan), an iPhone 6 with iOS 9.3, and iPhone 5s on iOS 9.2.

I used to send videos from my iPhone 6 to my Mac via Airdrop and it works perfectly (even vice versa). The following day, when I was trying to send from my Mac to an iPhone 5s, the iPhone is not showing on the Mac's Airdrop window and the Mac is not showing on the iPhone's Airdrop pane. So I tried activating my Airdrop on the iPhone 6 just to check or possibly isolate the problem. However, even the iPhone 6 and the Mac are not showing on each others' Airdrop device listings. I usually enable the Airdrop to be discoverable by Everyone at first but the iOS devices didn't detect the Mac and the Mac didn't detect the 2 iOS devices.

I tried rebooting all the devices (Mac, iPhone 5s, iPhone 6) and tried to activate Airdrop but still, the devices are not showing up. Am I correct that I just need to make sure that Bluetooth and WiFi are enabled? I also made sure that the iOS devices were NOT on Portable Hotspot mode too.

Is there something I am missing here? What is the best practice to assuring that Airdrop works smoothly between any device (iOS-iOS, iOS-Mac, Mac-Mac)?