I also have this problem.
Essentially, the Batuu locals are not wearing any alien masks at all. Mirialan and Zabrak face paint exists on some bald males and females with hair. Hondo Ohnaka is properly masked, though.
I have never used many mods to start with, but I tried all the self-help options before searching here.
To be utterly certain about my report, here is what I have done, in order:
1. I deleted (its backed up elsewhere of course) the entire Sims 4 folder from here: C:\Users\Username\Documents\Electronic Arts
2. I ran a Repair Game in Origin on the Sims 4 installation
3. I loaded up a brand new game that created an all-new Sims 4 folder, so, absolutely no mods, CC, or even a Tray of sims/lots.
4. I imported Babs L'Amour from my freshly created Tray of Maxis-included sims, and replaced the first created family with Babs for starting the game.
5. I placed Babs in an empty starter house in Oasis Springs.
6. I clicked Babs' phone and sent her immediately on a vacation to Batuu.
7. I wandered the zone for a while until a good number of sims had spawned in.
The local Batuu sims were in the same unfortunate state as before: "Batuu locals are not wearing any alien masks at all. Mirialan and Zabrak face paint exists on some bald males and females with hair." Reputation NPCs (Scoundrels, First Order and Resistance member NPCs) have appropriate costumes and helmets on, but no alien masks/headpieces among them, except for Hondo Ohnaka, who appears correctly.
I was JUST about to reinstall the whole game when I found this thread.
My system:
----------------
CPU: Intel i7-6700K Skylake at 4.18 GHz
GPU: nVidia GeForce GTX 970 with 4GB GDDR5 Samsung memory
RAM: 32 GB of dual-channel DDR4 3000 (four 8GB DIMMs)
MoBo: ASUS Maximus VIII Hero with Intel Skylake chipset and Z170 Southbridge, BIOS Version 1902
OS Drive: 1 TB SSD
Additional Storage Drive: 1 TB SSD
OS: Windows 10 Home 64-bit, build 19041
Update 11/15/2020: I decided to try a full reinstall. I have every expansion, game pack, and stuff pack. Except the hamster Pets addition. I don't have that. Anyway, I uninstalled the Sims 4. I reinstalled the game and all 24 Packs. I deleted my entire Sims 4 folder from my Windows Documents folder before I started, so the new game created a fresh folder too.
Again I started with Babs L'Amour and took her straight to Batuu.
There are still no alien masks.
I'll attach some screenshots, but my save file exceeds this message board's allowance, even zipped. If you want it, just direct-message me and I'll email it.