Don't think it's the heat, seeing as the other elm isn't having the same problem. I'll check the soil and if it's not that, then I'll try watering it some more.
Spot on
Just on a second thought. Would repotting it be such a good idea? If it's not the healthiest and its not the right time of year is it really a good option?
Dont repot until early Spring.
“Empty your mind, be formless, shapeless - like water. Now you put water into a cup, it becomes the cup, you put water into a bottle, it becomes the bottle, you put it in a teapot, it becomes the teapot. Now water can flow or it can crash. Be like water, my friend.”
This has got me thinking, although the trees mentioned are of the same species and one is effected while the others are not is it viable to consider that the tree is individual to itself and might not be happy in its current situation, where the others are fine? Like when one person says "I don't mind the heat" while another struggles with it? Like most things I guess there are infinite variables?!
Im with Siddhar on this one and i would strongly recommend that you do not repot now.
If new shoots are appearing, let these grow out and keep up the seasol.
A pot bound tree requires extra care but can be maintained and survive until it is the correct time to repot. Whereas a stressed tree, if repotted, may die.
Let us know how those new shoots look in a couple of weeks, they should be fine given Chinese Elm is a tough species.
There are many ways to do things, but only one "best" way.
I have a number of elms and this has happened to a couple of them. I cut off any leaves with spots on them/going yellow. Its seems to allow the tree recover better/quicker. Discard the leaves somewhere away from your trees in case it is some sort of pest/fungus,