Glow-squids and normal Squids tend to kill themselves by going onto a block above sea level. They always do this, and you can try this by yourself by making a pool of water, adding squids and just wait and see. Considering that this bug/issue has been happening ever since the squids were added I am probably not the first one to report this.
By the way, this affects the latest version PLUS the snapshots, and even the other versions too.
I realised that this is a duplicate of https://bugs.mojang.com/browse/MC-132473