Reimporting a sprite sheet that had sockets placed on some of the individual frames will result in the sockets moving if the sprite sheet's dimensions have changed since the previous import. This would happen during development if new frames were added to a sprite and the sheet size had to grow to contain them all, assuming that some sockets had been placed before the sheet size changed.
1. Export a sprite sheet from a program like TexturePacker and import it with Paper2D.
2. Add a few sockets to one of the imported frames. Put them at easily-recognizable places on the sprite.
3. Change the dimensions of the sprite sheet in the source program (e.g. TexturePacker) and repeat the export/import process.
At this point, the imported sprite's sockets will be in the same position relative to each other, but the group will be translated away from where they were on the sprite when you placed them. The expectation is that the sockets will still be on the same parts of the sprite, since the image itself hasn't changed.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-26889 in the post.