I’ve been connecting my phone to my laptop to watch youtube (essentially treating it as a second monitor) for a long time but when I updated my system it doesn’t work anymore. It disconnects only when It’s playing an audio and not when it’s idle, and it also affects the connection with my bluetooth headphones which is pretty weird. I think it’s a kernel issue as I first experienced it when I updated kernels (normal linux version and now with linux-lts).
It is probably wise to go through the whole process using bluetoothctl and remove the device and then scan and pair and connect and trust etc. Sometimes it will pick up the wrong hardware ID and not work properly. If you go through the complete process in this matter usually you can get it working.It may not necessarily be a kernel problem. It may be just that when a new kernel gets installed and it connects things go wonky. Bluetooth can be fin achy at best.