Airdrop Not Connecting

I am having trouble connecting with AirDrop, particularly between my iMac (macOS Sierra 10.12.6) and my iPhone 6 (iOS 11.2.6). I’ve had stages over the years where it wouldn’t work, then it would work, and then it would stop working again. This is particularly frustrating because AirDrop had become a big part of my workflow as a graphic designer and I really need it to function properly. I’ve tried searching for solutions and nothing has worked. Here are the details of what I’ve already tried:

• Bluetooth turned on for both devices
• WiFi turned on for both devices
• AirDrop turned on for both devices and set to “Allow me to be discovered by: Everyone”
• Firewall turned off on iMac
• Logged in with the same iCloud account on both devices
• Restarting both devices
• Updating both devices

I’m really without a clue as to why AirDrop isn’t working and was wondering if anyone can help me. Thanks in advance!