Changes to the sort order do not revert the order of inputs on a node when undone. It will change if the node is refreshed or the graph is saved, however.
1) Launch AudioQA
2) Create a new Metasound Source
3) Right-click on the graph and search for "MSS_GrainDelay" Note that the Array input appears on the top.
4) Double click on the node to open its graph
5) Under Inputs, select Array
6) In the Details Panel, set the Sort Order to 100
7) Go back to the MetaSound Source you created. The Array input is now at the bottom of the input list on the node
8) Ctrl + Z to undo your action
The node input order returns to how it was previously, with Array at the top
The Sort value changes, but the order of the inputs on the node do not change
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-170107 in the post.