Headphones won't connect to Bluetooth (not a pairing problem)

Using Plantronics Bluetooth headphones (S5xx17). When they have been turned off, the only way they will reconnect to my BT source is by opening the Windows 10 Sounds panel (not the Settings>Bluetooth and Other Devices window that shows them paired) then selecting the Playback tab. In that tab I have to right-click the icon for my headphones, then click Connect. At that point the headphones will connect to Bluetooth.
I have a BT radio that simply connects to the same BT setup when turned on. I don’t understand why I must go through this ritual each time I power on the headphones. Am I missing some setting or is it just the way the headphones are designed?

99% of the time is an issue with BT driver , try to update it and if it is up to date you haven't mentioned if you are on a laptop or not as the manufacturer might consider further tweaks to strict battery usage on conservative battery profiles (constant search for devices might consume power) where a fix might simply be changing your power plan to a less conservative one (Try Balanced or High Performance maybe)