First, start by just trying to restart your phone and check for update. A new version of software update with the Android Pie is available it should help with Bluetooth
If it's not working try wiping cache.
It should work because my galaxy watch and Bluetooth speaker/earphone are often connected simultaneously.
Could you please elaborate on what kind of issues you're experiencing? Your S9 should be fully capable of connecting to two Bluetooth devices simultaneously.
The suggestions made by @MAP are a good place to start, so maybe give those a shot and report back if you're still running into problems 😊
