Elegoo Centauri Carbon Vented Riser Vent-Lock

Print with orientation as shown.

Insert as shown with whichever side is needed. 
Top of device (right-way-up) is indicated by the 3 little grooves (for texture).

I used one while printing and it didn't fall out, but your experience may vary.
If it's being shaken loose, a solution might be printing with TPU at about 103% so it can be “squeezed” into place w/more friction. I've not printed with TPU yet, but when I do, I'll see how it works.

Let me know what works and what doesn't.