Shelob Tolkien - leaves slowly turning yellow and dropping

[Spiffy]

Hi All...wondering if anyone can help with this plant.

I purchased back in Sept and plant looked healthy and with a flower spike. Within a couple of weeks the flower spike died off and the first set of leaves dropped.

I figured it may be too cold or not enough light, so moved it under a grow light in my kitchen, which is a bit warmer (say 14c - 20c daily variation). Humidty is 60-90% (gets steamy when cooking!). The grow light is decent and we have a chili plant and herbs also growing under there. The plant seemed to be doing better and a new bulb growth has appeared.

Attached are 3 photos. First from when I bought it, the 2nd two from this week where it looks like it's going to lose another set of leaves. I'd just watered it over the weekend so now I'm suspecting it's either our water or fertiliser that is giving it grief. I use a mixture of tap and rain water, depending what's on hand. Fertilise monthly. Roots look fine and even showing some new root growth.

First time growing one of these so not sure if anyone has any tips? Successfully kept Nepenthes, Phals and Paphs so a bit stumped on this one! Main issue we have is living in a cold draughty house in the UK, so can be cold and not much light in the middle of winter. I thought these plants were supposed to be relatively forgiving!