I never had Bluetooth connection issues with my Logitech hardware, but I wanted mine to work without an OS (i.e. with a Bolt receiver).
Solaar handled the pairing in 30 seconds flat, and I can't be happier. The only thing is, since Bolt doesn't look like proper BT to the OS, battery levels can only be monitored from Solaar itself.
IIUIC, Unifying receiver used a completely different protocol, but Bolt protocol is just supercharged Bluetooth with some low latency and encryption sauces on top.
Sounds nice, except so far I have only one Logitech device that works with the bolt receiver, which is the MX Master 3s.
I also have an MX vertical which uses the unifying receiver.
Then I also have a pro x superlight, which has yet another receiver. I believe they call that one lightspeed or something.
So now I have 3 separate adapters for 3 devices, all of which theoretically support pairing multiple devices (I think the lightspeed only does 3 though).
It also introduces a ton of lag, especially when more than a single device and some distance is involved (Mouse + Keyboard + Headphones makes my headphones cut out sometimes)
Bluetooth Low Energy with some Logitech sauce added into it. Apparently encrypted and marketed for use in contexts where FIPS level security would be required.
Solaar handled the pairing in 30 seconds flat, and I can't be happier. The only thing is, since Bolt doesn't look like proper BT to the OS, battery levels can only be monitored from Solaar itself.