We Have a 20 Year Old Ash Tree
At the very base of the tree there is a small soft spot, large enough to put your finger in. What could this be?
It could be collar rot. This article discussed collar rot on maples: https://www.gardeningknowhow.com/ornamental/trees/maple/maple-tree-bark-disease.htm
It might be borer damage. https://www.gardeningknowhow.com/ornamental/trees/ash/emerald-ash-borer.htm