I've been having problems with my phone Everytime I connect any Bluetooth device, at first it works just fine but as I continue to use apps that require WiFi, the phone loses connection with the WiFi, while it doesn't completely disconnect from the WiFi, the phone doesn't connect back to it even though I know my router is working just fine. This only happens when I use Bluetooth devices, and I've also tried other Galaxy s9 phones with the same Bluetooth devices and those don't lose connection, which makes me believe that it only affects certain phones. Only sort of solution I've found is to turn off WiFi from settings and turn it back on, but this only fixes the problem for a couple minutes before I need to the same process because I lose connection again. And to be sure I did the same with cellular data and everything worked fine, so the problem only happens with WiFi.
Have you tried resetting the network settings? Just a heads up, by resetting the network settings, it will remove all wi-fi and Bluetooth settings you currently have saved.
Have you tried resetting the modem for your internet?
I would recommend taking your device to your local UbreakIfix so they can get a hands-on look at your device to see if there are any settings causing the symptoms you are experiencing.