May be due to bluetooth versions.
Try this:
- delete all pairings
- turn off bluetoth of everything
- reset the headphones
- pick a device which would not connect, say the tablet, turn it’s bluetooth on, pair with it.
If that works, solved it then
- turn off the bluetooth of the device above
- turn headphones off, wait, on.
- turn on bluetooth of something else, pair with it.
If that works then repeat for your devices.
If it works then to swap devices which are of a different bluetooth version
- turn off bluetooth of connected device
- turn headphones off/on
- turn on bluetooth of next device, connect to it.
You don’t need to do this normally all the time, only when you connect to a bluetooth device then try to connect to an older bluetooth version. Also try to connect to oldest bluetooth devices first.
The root cause is subtle, because of the app which you connect to first, your phone is usually the newest bluetooth version, once the headphone connects to one version it cannot then connect to an older version without turning off then on. That exact combination of events of new then old without off/on is rare so it’s not a common issue but some who tried exactly what you did get tripped up.
Also note Windows 10 once it is paired tries to connect without your asking it to, so combined with the above can cause bizarre outcomes.
Also some comments here is their other bluetooth items don’t have this problem, well that is because they usually are older bluetooth versions so they are connecting already at older versions even when you connect from a new phone, so it’s an issue caused by owning a newer bluetooth audio product alongside new phone and older devices.