Why doesn't the Sync button work?

I've been using my Switch Pro Controller to play Elden Ring on PC and every so often it wouldn't be able to connect to my PC via Bluetooth, so I would just reconnect it. However I picked it up yesterday and had to reconnect it like usual but this time the Sync button on the front of the controller isn't working anymore, usually the 4 dots on the bottom of the controller strobe while it's connecting but none came on. It should be noted that all the other buttons turn the controller on with the LEDs and everything, any thoughts?