Here's a post about chinese elm:
https://www.helpfulgardener.com/forum/ ... lm#p417551
shortening hours of daylight may be triggering it in to dormancy. It probably isn't getting enough light where it is, anyway. If you want it to keep its leaves (not drop them like deciduous trees), you will need to arrange supplemental lighting for it. Even putting it on a good south facing window won't be enough as days get shorter.
Supplemental lighting is a dedicated fluorescent light, shining on it from just a few inches away:
Otherwise, you can let it go dormant, put it in a cool dim part of your house, give it minimal water and no fertilizer and wait until spring.