Doubt that is any disease you need to be concerned with. Horse chestnuts are not at all drought tolerant and dry conditions in summer generally lead to scorched leaves and general foliar deterioration. The 70 y.o. one I inherited with my current garden looks much worse than that after our normal very dry summer and has dropped many leaves.

HERE is my post on this topic, sorry so many of the pix are deleted.

its september.. days are getting shorter.. and trees are shutting down..

the result of shutting down.. is ugly leaves..

we do not treat leaves that will fall off in a few weeks or a month ...

trees that are stressed.. can shut down early... stress might be heat.. drought.. hail storm etc.. related.. everything that happened to the tree since the leaves emerged.. causes ugly leaves in fall .. care to tell us what this trees been thru since early spring???

bark maturation and weirdness doesnt really bother me... nothing you can do about it.. other than observe it....

but.. could we see the whole trunk.. including where it goes in the ground.. is the root flare apparent??

ken