When you have a server side resourcepack on your server and a player logs on and downloads the resourcepack by hitting YES on the prompt on server - they get a resourcepack named "legacy" and that's it.

It used to be called "Myresourcepackzip" when downloaded.
Then after some update and changed by Mojang it became "legacyMyresourcepackzip".

And now? Now the problem is that it's just called "legacy" and the "Myresourcepackzip" part is missing completely.

This results in the "legacy" getting overwritten every time you log in to some server that has a server side resource pack.

Even though nothing has been updated you now end up downloading the same data again and again and again.