Sometimes there's some inconsistency between local types and structs view.
Typically, you can see the type in the "Structures" view are zero-lengthed, which should normally be the same size as local type's one.
When this happens, you'll not be able to rename the structure fields in HexRay Decompiler's view, and both hotkey N and right-clicking the item won't show the rename popup.
After reverse engineering the hexx64.dll, I found that IDA tries to do the following things: