I am active, I've just been busy with stuff (Life).
I will be updating Simple Sit soon.
Currently there are only a few bugs players can glitch through the floor by spamming /sit, and sometimes mini armorstands are left behind (I'm still working on this one, I'm unable to recreate it).
Players not being able to see themselfs while laying is not a bug, it's how I implented the lay feature. I will be changing this in the future.
If there are any bugs/glitchs I missed please let me know in the discussion page.
There is more infomation in my recent post in the discussion page.
https://www.spigotmc.org/threads/103915/page-5#post-2656713
Thank you for using Simple Sit. :D