This is when an hearthling mine the last block where stand another hearthling. In such case, hearthlings should fall just like ore.
Meanwhile the bug fix, you can put a ladder to help them return to the ground.
(As I’m unsure if this bug is already into the bug dev’s list, @sdee, could you have a look?)
Does anyone have a good way to reproduce this? I can’t seem to make my hearthlings float.
I’ve managed it a few times. The easy way seems to be to dig a cavity underneath a single layer of dirt/stone, the larger the cavity the better. Dig a two block wide trench on the surface (one block over the cavity, one block on dirt) around the perimeter of the cavity and when they almost have that trench dug, highlight the entire remaining surface area as a mining zone. This should trap your hearthlings up there and some should get caught/levitate
And to add to what @Boulderboy said, don’t do your mine test with 2 hearthlings but with many more to have more chances to get the situation.
I tried a few times this way, but still no luck.
I just tried it again before I shut down for the night. I can’t seem to get them to do it now either lol. They leave one block below them currently, but once in a while they mine that block out and then turn into hover-hearthlings. I’ll see if I can get them to do it tomorrow and I’ll make sure to note exactly what they were doing
Same here, could not replicate this in a simple mining test. I wonder if it’s not linked to some AI lag (at lunch time or if a priority task like harvesting berries is sent). Investigating…
Still no luck! 
Could that thing appear after a specific error?
I’ll try a few more things…
I just had the exact same issue. What caused it for me was similar to what boulderboy stated.
I had mined out an area, that had a single block thickness roof and decided I would clear the roof away, to make it easier to see what was going on in there. Several hearthlings mined the roof away, but the one in the picture was the last one there and was stuck on a single, floating block, which she then mined, leaving her floating in mid-air.
That’s odd, whatever I try I don’t get it…
@stormknight what was the tool used to get the roof down? 1x1 or 4x4?
You say she mined herself the block under her feet? No other hearthling in the zone at the moment?
I’ll try another quick test using the same save. Will post shortly.
Ok, I loaded that save. On load, I got the following error message:
develop-2521 (x64)
radiant/modules/entities.luac:86: attempt to index local 'entity' (a nil value)
stack traceback:
radiant/modules/events.luac:68: in function <radiant/modules/events.luac:65>
radiant/modules/entities.luac:86: in function 'get_world_grid_location'
stonehearth/services/server/town/town.luac:97: in function '?'
stonehearth/services/server/town/town.luac:30: in function '_restore_saved_calls'
stonehearth/services/server/town/town.luac:11: in function '_on_game_loaded'
stonehearth/services/server/town/town.luac:9: in function 'obj'
radiant/modules/events.luac:15: in function 'self'
radiant/modules/events.luac:80: in function <radiant/modules/events.luac:78>
[C]: in function 'xpcall'
radiant/modules/events.luac:78: in function <radiant/modules/events.luac:70>
I then replicated the problem and recorded doing so. Here’s a link to the video:
@stormknight, great feedback! I tried to reproduce the situation on your vid using 4x4, roof and all but no way, all my hearthlings just fall correctly. Now because it’s a new game, I don’t have any error on load. Could it be related?
I don’t know. I tried again and I can 100% reproduce this.
Things to note:
- This is a save I’ve played for about 4-5 hours, so there’s around 20 Hearthlings, plenty of buildings etc.
- I’ve switched the viewer panel on to show LUA usage etc, in case that helps.
- Whilst it reproduces, it’s haphazard and sometimes they fall correctly.
The only thing I can think of is, is the code that handles falling getting cut sometimes because the game is too busy with other things?
Here’s an additional video at normal speed, showing the LUA/processor breakdown panel. In this one, one of the Hearthlings falls correctly, then seconds later, some get stuck.
If you can reproduce this systematically, maybe you should zip the save and send it to @Albert…
Save file for that game is here. This is the save that I was using for the above videos.
https://drive.google.com/file/d/0B39xSEui7iQXd1M1dVJjam9tLXc/view?usp=sharing
Not sure how to send it to @Albert - hopefully he will see it here! 
Great work @stormknight! Taking a look now.
Well, I fixed the bug loading the save game, but it was unrelated to the floating hearthlings which I still can’t make happen.
I repro’d this (unintentionally) without digging. A hearthling was placing a window on a second floor; and simultaneously, as he was going up the ladder to place it, another hearthling began removing the ladder the first hearthling created, causing him to get stuck.
Maybe try making a small two-storey building with a window on top, and stamp like 5 hearthlings inside while contructing