Since so little of it is mounted and most is just hanging free I am still betting it's underwatered. The pseudobulbs look a bit shriveled, so I would mount more of the plant. More lights could raise the temps. Really though, I'm thinking it's a lack of water issue since I have several bulbos outside right mow experiencing 45 degree nights and I haven't seen any yellowing or leaf drop
Your orchid could also be underfed. Yellowing of the new growth tips is a sign of non mobile nutrient defficiency, either calcium or iron usually. If it was a mobile nutrient issue the older leaves would be yellowing and dropping. I suggest a "weakly, weekly" fertilizer regime for your orchids since they aren't getting any frog ferts.