Brown spot help

I have had this Calathea Orbifolia for about a month now. It was doing fine but this spot on one leaf is slowly getting bigger. No sign of pests and I only water when the top 2cm or so is dry.

I did leave it for about 5 days when I went out of town last week. It was placed next to a window but I recently moved it under a skylight. It had a small brown spot (which grew into this) since it was at the window.