I have a problem with my xbox

I have a problem woth my Xbox Series X controller.

So whilst I'm gaming let's say on fortnite for example: so I'm in the middle of trying to snipe someone and my controller randomly disconnects but the lights are still on but slowely flashing, and the console just stopped detecting it. The firmware is at the latest version on controller and console, the batteries are fine... so could you please give me some ideas thar could fix that problem? I only really ever have 1 controller connected at the same time and it's really only less than 5 metres away from the console.

:)