Oh my goodness. I checked in the enemy editor. O tile is not set in respective enemy tiles for all enemies. Corruption is taking place.
Please set all enemies to the respective tiles. Fix it and release them in the next build! THIS IS HIGH PRIORITY!
EDIT: I think after Dark Nation had fixed the heart issue, all O and S tile moved down 56 pages.
Developers, for all enemies, here are the instructions:
Go to the enemy editor, double-click an enemy and click O tile. Note that the white selector is in the same position. DO NOT MOVE THE SELECTOR, USE PAGE UP KEY. Carefully move up 56 pages until you see the selector in the respective enemy tile. Do the same with S tile.
Please do ALL enemies. Again this is for proposed 2nd and proposed 3rd.
It's going to take a lot of work...
Uh... no thanks. We'll revert proposed2nd and proposed3rd to what they were in the last beta, and try again 😊
As DN fixed the heart issue, I want to wait and see if he has any idea what caused the corruption, though.
Okay. Last build was 528 (530 macosx).
All right, Dark Nation, lend a response on what caused the O Tile, S Tile, and E Tile(E not used for official quests) for all enemies to move down 56 pages after you fixed the heart issue.
This bug is verified for the moment in 536. 
I made a mistake. It's a bit technical so I'll go into it only if people really want to know the logistics behind the problem. Needless to say, it's not a bug but an error on my part.
Any plans? After you reverted to the ones in 528 and tried again, here is to check:
heart in bottom left minitile in tile 0, and
quest rule OFF: correct offset enemy weapon collision detection
These are the two that you are doing to update the proposed 2nd and 3rd.
Well done.
Enemies are visible and yes, checked it shows a heart and the rule remain unchecked.
Fixed in 564. R.I.P.