Same to me, and I played local copy version since 3 days ago. I didn't met missing face bug until today just afk for a rest. After that I just restarted the game then this bug happened. It's more like a timed bomb. Most confused me is everything I run are local version.

Okay for now I can figure out how to fix it yourself.
1. Subscribe Character Editor mod, enable it.
2. In game, check your pawn who missing face. The "Skin" parameter have 4 sliders (RGBA), A means alpha aka transparency.
3. For a buggy pawn who missing face, 4 parameters of Skin must been reset to 0 (most left) somehow.
4. Manually Change those value, you can switch to a facial normal pawn for reference.
5. Now should be Okay again, I hope.

Note:
This method also help those pawns who missing their hairstyle. Use same way to fix Hairstyle's parameters.
What action causing this bug still unknown for me. Just noticed those parameters have been reset. While alpha reset to 0, face or hairstyle means transparently.

引用自 Ryusa：

Okay for now I can figure out how to fix it yourself.
1. Subscribe Character Editor mod, enable it.
2. In game, check your pawn who missing face. The "Skin" parameter have 4 sliders (RGBA), A means alpha aka transparency.
3. For a buggy pawn who missing face, 4 parameters of Skin must been reset to 0 (most left) somehow.
4. Manually Change those value, you can switch to a facial normal pawn for reference.
5. Now should be Okay again, I hope.

Note:
This method also help those pawns who missing their hairstyle. Use same way to fix Hairstyle's parameters.
What action causing this bug still unknown for me. Just noticed those parameters have been reset. While alpha reset to 0, face or hairstyle means transparently.

I've tried that but these settings do not allow me to change face type, and moving sliders changes only the skin color, face is still invisible. I do see the hair or eyes/eybrows but the rest of the face is transparent

However, I am still able to change other pawns' faces through character editor menu

Maybe missing face textures. In short you should copy and paste face textures to make sure they have all types.
For example I use Gynoid:
Originally it only have Female_Average_Normal.
What you should do is copy this type 3-direction files to create following prefix files:
Average_Pointy, Average_Wide, Narrow_Normal, Narrow_Pointy, Narrow_Wide.

I know this thread is aged now (10 hours old as of writing), but I've been having this same issue as well. Just leaving this here in case something new happens.

Yesterday I've talk to him personally, following are archived messages, maybe helpful for any other people have same problem:

For Vanilla game, any gender of pawn use 2*3 (Average, Narrow; Normal, Pointy, Wide) different type of face shapes. Humanoid Alien Race codes force the extend races use the only one type - Average_Normal. In some case this bound broken, leading a pawn being use a wrong face type, that would cause missing textures.
So you need is to local mod folder and create those face types manually.
I use Mod Manager to make local copies to keep mod stability, and debug with local edting. You can try this way too.
For example Android Tiers, I use this mod too so I can figure out the path.
RimWorld\Mods\Android_tiers\Textures\Things\Droids
* This path is local copy version created by Mod Manager, for Steam managed folder you should search workshop ID folder. I highly recommend use Everything, a external file searching program for a quick search.
Android tiers have several tiers as it is. Each tier folder have its unique texture, with same structure.

I've test something and find a interesting thing.
Hair and Head parameters will be reset to all 0 if you use Character Editor to set any slider's value excess 255.
if Alpha set to 0, pawn's head or hairstyle will be change to transparent.
And if start a new game with this data (maybe auto random generated), pawn's appearance looks fine, but if you load the game, their head or hairstyle are missing.
This means, no matter if you use Character Editor to change color for a better look (or Change Mirror) or not, any behaviors trigger this will leading this result. So you can use Character Editor mod as a safe, since it can change alpha slider to make hairstyle and face appear again.

For now I am using that Character Editor feature, however, this is not a 100% solution and mechanics are still bugged, new raiders/wanderes entering the map still have a chance to be faceless. The thing that works for me is saving and pasting that pawn (pretty much duplicating) and deleting the bugged one, be aware though that the new pawn behaves like new one (loses all of its relationships etc.)
Probably modders who have more skills than me will be able to find a better solution :)

Was never able to replicate these issues. And they are pretty isolated to begin with as well as happen randomly in running games after several hours. Not something I can really debug, can only say so far pretty much everyone who reported it ran prepare carefully or change dresser.

it is change dresser, just checked for all the people who have that turn it off and all faces should return to normal