I entered in the command
/fill 528 53 527 543 65 527 slime
on a superflat world, and the game crashed right after placing them. I reopened the world and the wall of slime blocks were gone. It happened multiple times, so I tried to fill it in by hand. Then the game crashed when I placed a Slime Block at 538, 62, 537. It also happened at y=63 with the same xz.

I don't know if this is a duplicate, because I don't know what exactly happened, and do not know what to search.

I hope this was good enough information to recreate the crash. I also attached the crash report, if that helps. If it doesn't crash, try flying around the Slime block. It doesn't do it instantly.

Also, if the Slime Block is still there when you log back in, break it instantly or you may crash again.