one time I was going to remix a game griffpatch made called Minecraft and I went to costumes and changed a lot of costume to vector and changing it until it stopped saving, I tried saving it again but still does not work. why is it not saving?

To answer this question, first we'll do a size comparison:

As you can see, the vector costume is bigger than the bitmap costume because converting from bitmap to vector still uses the old bitmap costume, it's just embedded within the new vector one.

Now about why the project no longer saves. I believe this could be a network issue. Paper Minecraft is a very, very big project and big projects tend to have difficulties saving. Increasing the file size doesn't help it save, which is probably why it stopped saving after you changed a ton of costumes to vector.

So a bit of advice, don't change the bitmap costumes to vector. They won't look better because they're technically still bitmaps.

Thanks