Not Austrian, I believe it is either Bulgarian or maybe Hungarian. It is not intended for an S84/98 bayonet nor was it ever used for that bayonet but it fits fairly well.
I've looked at all the Bulgarian/Hungarian frogs I can find pics of, and haven't been able to find another one like this one. Still trying to find out what it is?
You may be correct but remember that there was a lot of variation in frogs used by both nations during different periods for different bayonets. Austria was the same.
I still can't find a pic of another, but the general shape is of an Austro-Hungarian Mannlicher frog?
Is there a missing post in this thread?
There was one earlier that said it was a "self made" frog, and now is seems to have vanished?