This covers both facial expressions, & gagged mouth. A gag mouth is a facial expression.
For both...
If using SE/AE, make sure you've installed the correct version of MFGfix (see installation steps for link) and check SE versus AE Version Trap.
IF using LE, make sure you've installed Mfg Console
If it's not MFG, it could be the Racemenu bug. It happens to other mods providing expressions too. See cure below
For Gags... (first MFG & Racemenu must be working as above)
In the Toys&Love MCM - Effects 1 Tab, you can change "Gag Mouth Open Size" to adjust for some cases
Most gags don't support beast races
If you have a mod that changes the head, including some race mods that change the head, chances are high that it's not compatible
Racemenu bug Cure:
Open RaceMenu (console command ShowRaceManu), and go to the Expressions tab
Move any slider, and you will see the face change (if you don't see the face change you have bigger problems)
Move the slider back to zero. Exit. Done. It's fixed now
This cure will normally keep it cured until starting a new game unless or when swapping profiles with a mod manager.