I have had this happen multiple/many times.
Most of the time it happens when I am editing the title of an action that is being referenced by another action. More specifically when the action is referenced in an expression that I had to type the title into.
Whenever an action title is renamed, the dynamic values for that action usually automatically rename. However, if the action was in an expression that wasn't using the dynamic content, it doesn't always change.
I think the flow is stuck in some kind of name checking limbo. Like it wants to let you rename the action, but there are other steps that are specifically referencing that action which will break if the name is changed. It can't auto update those things in the expression, so it just keeps acting like it is in the rename state.
When it happens to me, I put the name back the way it was and click save. Then (if it lets me save), I will back out of the flow, click refresh, and completely close my browser. I'll come back into the flow and hopefully it will let me work normally.
Otherwise, I'll have to go through the actions below and delete any references to the original name and redo all of them.
