When both Joy-Cons are docked at the workstation, the left and right Joy-Cons disconnect when input is received from the other Joy-Con (the right Joy-Con disconnects when the left Joy-Con receives input).
The Joy-Con disconnects when input is sent to the other Joy-Con.
Replace the Joy-Con side rail causing the disconnection problem (you’ll also notice the connection icon in the lower left corner of the controller causing the disconnection, indicating it’s wirelessly connected, even though it’s docked).
This problem could also be caused by liquid damage at the connection points or on the ribbon cable—first check if the liquid can be cleaned with ISO (isolation) to resolve the issue. If nothing changes, then replace the affected component.
