I had a similar situation last summer. I moved my Chinease Elm inside for a week, with an aqua globe, while on vacation in September. Returned and half the foliage was gone and the remainder was yellowing. I thought it was root-bound (it was), so I trimmed the roots, re-potted and inspected. I also found a Spider Mite infestation; I believe being indoors allowed any mites that were there to multiply and thrive. I treated the mites with Neem oil, a foliar spray once every 5-7 days, dousing the tree heavily and ensuring to get the undersides of leaves and also the soil. 1.5 TSP. Neem to 32 OZ of water. I also moved the tree back outside, but in the shade to recover until the roots were able to keep up with transportation, then back in the sun. Surprisingly, it had a small flush of growth before going fully dormant the end of December. Outside all winter, close to the house. During very cold snaps (here is mid 20's) I would wrap the pot in a couple towels to protect the roots and that's it, since by noon it would warm up usually to above freezing. I did not bother protecting from frost until the buds began to burst. I potted to a larger pot this spring and bare-rooted the tree. It has a flush of healthy new growth and leaves. I would say, being outside and allowing it to go dormant is healthy to the tree. I'm unsure of what kind of lighting you're providing. I seem to do ok with a Westward, outdoor balcony. Shaded in the morning but lots of bright afternoon and evening sun. Watering is imperative, though, in summer with these conditions. Maybe with a picture, a more experienced grower will be able to assist.