Hi all, I was wondering if you could help me identify the cause of what appears to be random leaf yellowing and drop on my Meyer Lemon tree that's in for the winter. See two examples below:

Every week or so since maybe December, I've lost two-three leaves on my tree. They never seem to be at the bottom, which is where I would normally expect to see issues from overwatering, and I'm only watering once a doll rod comes out dry just about everywhere except the very bottom.

The tree is planted in ~40-50% pine bark fines, 20% perlite, and maybe a 30-40% mix of compost, potting soil, and manure, but most of the pot is the soil the plant came in from Four Winds Growers. It dries fairly fast, around a week even indoors, and I have a wick hanging from the bottom to help prevent a perched water table in the soil. I have probably 14 holes drilled in the bottom of the pot. When I water, I water until the soil is evenly moist. Quite a bit. Clay pot suspended in a glazed pot.

In the last month and a half, I've probably used a tiny bit of Foliage Pro twice.

Temperatures in my home range from 63 to 68 degrees. Humidity typically ranges from 34%-44%, dropping when I'm away. I've started to run a humidifier again to maintain a constant 40% nearby. It rarely has to run. Soil temperature is 66 degrees currently. Leaf temperature is 63-65 degrees depending on how close to the window you are.

While the plant is in front of a SW sliding door, sunlight is limited in Wisconsin in the winter, and I live in a city which further limits light. I was almost assuredly not getting it enough light, but recently installed two of these grow lights, and it seems much happier:

https://www.amazon.com/gp/product/B07NP1H25N/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1

They're on for probably 12 hours a day. Depending on where you put the sensor, I can measure ~20-50 kilolux at night.

When I first got the plant, I almost immediate found 1 mealybug on the plant. I have since only ever found one more. I know, I know. You never find just one mealybug. But I swear, that's the case. Removed, and plant washed with rubbing alcohol + water.

In the week before I got the grow lights, I noticed a minor spider mite infestation. Half a dozen washes mostly of rubbing alcohol + water, a few of baby soap + water, and I haven't seen them for maybe three weeks.

What is CRAZY is maybe once a month, I'll see a single drop of honeydew on the plant. Like one single aphid or mealybug had a snack. But no recognizable signs of any bugs!

I've treated the soil with nematodes twice just because I saw these guys, and I couldn't tell if they were mites or soil aphids.

The soil I added to the pot upon receipt was microwaved.

I have clearly tried a lot of things over the course of several months. So, that said, any idea why I might be getting this discoloration and leaf drop?