Mini dendrobium yellowing leaves!

Hi,

I've had this mini dendrobium for almost a year. It's pushed up two new pseudobulbs and one has put out a new stem and buds! It hasn't flowered yet, but some of the leaves on that bulb and an older one have started yellowing and falling off...

Kinda freaking out, just want to know if this is normal leaf sheading. It is in a western facing window, in a humidity tray, and I water once or twice a week. Any insight would be very helpful. Thanks!