iPhone hotspot using Bluetooth drops paired devices (iPad or MacBook) after about 10 sec

I set up an iPhone hotspot using Bluetooth but it drops paired devices (iPad or MacBook) after about 10 sec. This issue developed suddenly. I didn't have this problem before. Well actually I did but it would connect for 10-15 min before dropping so it was livable. Now no longer. Any ideas how to fix this and what happened?