incorrect 'unknown' tiles?

I had a similar problem yesterday:

 

I thought I had made another, more recent screenshot, where I opened up the area with the geyser, but it appears not. Can't make one now due to the game currently crashing on launch, but the dupes can come almost directly to the "unknown" tiles and they're still here.

Output log:

 

Initialize engine version: 2018.4.14f1 (05119b33d0b7)
GfxDevice: creating device client; threaded=1
Direct3D:
    Version:  Direct3D 11.0 [level 11.1]
    Renderer: AMD Radeon HD 8400 / R3 Series (ID=0x9830)
    Vendor:   
    VRAM:     2399 MB
    Driver:   26.20.12028.2
The resource Internal-ErrorShader.shader could not be loaded from the resource file!
 
(Filename:  Line: 1225)

The resource Internal-ErrorShader.shader could not be loaded from the resource file!
 
(Filename:  Line: 1225)

The resource Internal-ErrorShader.shader could not be loaded from the resource file!

(Filename:  Line: 1225)

looks like it's in the same physical spot in relation to the geyser, which is revealing.

I've seen these UNKNOWN areas even in the base game...

I have a two block unknown spot, and I've gotten the dups to dig around it entirely.  Still didn't reveal it.  I also loaded up the game with debug mode enabled and had the dups dig those very tiles.  When I switch back, the spot is still unknown.  

Melt the ice. Send a dupe in. Revealed.

Thats a bug known from pre-early-access.

I think this is attached to that geyser, because I had the same 2-tile hidden area bug in my base and was near the salt geyser. Super annoying, because I *really* wanted to build in the hidden area.

let it melt and then you can build on these two spots.

Can confirm - the same spot as author's is unrevealable (relative to the salt geyser)

Besides melting with heat, there are other ways to mine natural tiles protected in this unknown area.

By building a part of the building so that it hits an unknown area, it can be forcibly mined as part of the construction work.

Spoiler

Alternatively, if you can make a Robo-Miner, you can use it for mining.